Since there is technically a possibility for the HUN-HAT to escape the Demiplane of Basements he trapped himself without any exterior intervention while keeping the possibility to cast Twinned Mind Blank, I'll suggest it (and not wait for the OP to propose it, we'll do that quickly). Here is the setup, as it involves the DMM clone to cast planeshift herself, which she can do only once as she can't regain spell slots and has memorized only a single planeshift. We'll also elaborate on the fact that the DMM clone is a personnal acquaintance of Alfred, since it was established that she could make him a quarry for her retriever.
Memorized spell for the day : 5th level : Scry x3 as usual, 4th level: Dispel Magic, 8th level: Demiplane, 9th level: Gate. The rest irrelevant.
Simulacrum spell slots: 1st and 2nd: magic missles, 3th and 4th: fireballs, 5th and 6th level: Counterspells and Dispel Magic (half), 7th level: delayed blast fireball, 8th level: irrelevant, 9th level: Wish.
Alfred was puzzled. Ilmater just knocked on his door, had a cup of tea and asked him to murder a guy in cold blood because he was in an abusive relationship somehow. Over the last few days, Alfred had tried, several times a day, to Scry about this guy Ilmater had described but never identified clearly. All those attempts failed. He was starting to think it was just a prank.... But today, he would take a break for the chore of trying to locate this guy, who had left no impact on the world so far. His investigative skills revealed nothing, proving that he was most probably interacting with no one, and maybe even dead, to foil Scrying this way. So, it was time to indulge into one of the guilty pleasures in Alfred's life... Everything was good in his life, he had no motive to complain, but he had always felt guilt for the way he acted with Eilirilia. Since he had been doing Scrying attempt repeatedly for weeks, it occurred to him to Scry upon her, in order to see if she was still alive and well. So he proceeded to cast Scrying upon her.
In the past, Scrying was a 3rd level spell. During the Great Edition Change following the Dread Fourth Age of which all records had been erased, the Goddess of Magic decreed the spell was to become a 5th level spell. She had been moved by the petitions from the girls in the numerous school of magic who had learned that the teenagers boys were spending their time in their dorm chaincasting Scyring in their showers and locker rooms. Since this change, it required a lot of magical knowledge and maturity to cast it... Alfred was however easily able to chant the words of the Scrying spell, for his command of magic was peerless. His silvery mirror soon showed the image of Eilirilia. She wasn't protected by a Mind Blank, so he knew, for once, that he would succeed in scrying. It was also a way to confirm his mirror wasn't cracked or defective in any way...
Eiliria was in company two similar-looking gentlemen, twins, probably. He raised the volume and heard part of their conversation. It was obvious one of the twins was the commanding one, as the other was very passive, just taking orders, exactly like Eilirilia was. Suddenly, the assertive brother said that he was detecting a glowing scrying sensor and ordered his group (DMM, Simulacra and 6 galvan magens) to start destroy everything on the path indicated by the Retriver he ordered Eilirilia to summon. "Man, this guy is a dangerous moron if he thinks he can accurately follow a bearing like that..." I really need to save Eilirilia from him! That's why Ilmater sent me!" Alfred at this time was unaware that he hadn't seduced a Drow Priestess but a mere clone... It would need an immediate intervention. He considered going himself, but he had a tea appointment with Binky later in the day and he wouldn't miss that. Fortunately he was under no time pressure. By a crude calculation, he determined that it would take months of hovering to "reach him while destroying everything in our path" as HUN-HAT yelled in the mirror. However, the first measure would be to free Eilirilia and try to understand what happened. It would need not to harm her, despite her being somehow enthralled to obey HUN-HAT, whose name was still elusive to the whole world.
Casting its 8th level demiplane spell, he opened the shadowy door from the closet under the stairs leading, not to his usual extraplanar laboratory, but to a darker demiplane. The cell. It was unpleasant but he'd reason with Eilirilia once the threat had been removed and he'd explain her it was necessary to put her under key while he dealt with HUN-HAT. He hoped she would forgive him. After instructing the butler to prepare for the worse and to get back to him in the demiplane through the door a few rounds later, he began casting his 9th level spell, he created a Gate, calling for Eilirilia. Since the spell required concentration, the image in the mirror, back into his smoking lounge, suddenly stopped. Around the DMM's Simulacrum, a door opened and she was pulled inside to the cell plane. It was not an horrible cell, juste a bare, stone room with a few amenities like food and a bathing area. Sure, there were manacle chained to the wall, but it was more for show than anything: the demiplane itself was holding the creature trapped safely. Using his move action, Alfred got back to his cottage's dining room and closed the door. The butler simulacrum, nicknamed Butler 432, proceeded to cast dispel magic on the door as he had readied his action for, trapping Eilirilia inside, and used his move action to cross the Gate and fly away (using his haste action and bonus action to increase distance). Back in Alfred's cottage, using no action, Aflred dropped concentration on the Gate, completing the closure of the cell demiplane. Lacking any mean of extraplanar transportation, Eilirilia's Simulacrum was effectively trapped forever.
On the other side of the Gate, it's time to roll initiative. With the ability to add his INT bonus to iniative granted by his Temporal Awareness, his above average Dexterity and his ability to get Lucky thrice if needed, we can safely assume that Simulacrum get the initiative. It only matters for the HUN-HAT, because the Simulacrum always act at his turn and the Magen are still under order to perform Search action for invisible imaginary threats each round and they won't be around when their initiative count is reached.
Since the Simulacrum had taken the time to walk the path of extreme prejudice, he was armed with truesight. Therefore able to detect visual illusions, he immediately saw the Simulacrum for what it was truely, a mass of snow animated by magic. Sure, it was protected by Mind Blank, so no divination spell could be used on it, but Alfred's butler was the target of the True Seeing spell, not the HUN-HAT or his simulacrum.
Using his moves, the Butler closes the distance, then proceeded to Wish for an 8th level Symbol of Insanity triggered by the presence of a creature (it doesn't matter, the goal is to trigger as soon as the spell is cast). Everyone is included into the effect area. He is ready to spend a Convergent Future use to ensure the failure of the counterspell roll of HUN-HAT (since HUN-HAT has Wished for Mind Blank, he can't cast it to 9th level and ensure success), another for the counterspell roll of the Simulacrum (should his own counterspell fail against his counterspell), and two more, nearly kililng him if needed, to ensure both HUN-HAT and his cloned croney (let's call him Clowney)'s failure. Both are reduced to gibbering idiot status for one minute (not that it changes something for HUN-HAT, thought Butler). The 6 galvan magen most probably failed (+1 vs DC19) but one or two of them remaining won't kill Butler 432 in one round should they end up within range. Butler 432 will then proceed over the next 10 rounds to fireball and magic missile everything to death, moving, at half-speed, quicker than the magen can hover (should they keep their orders and not try to make sense of the gibberish orders given by their insane master. Butler 432, his mission accomplished, will keep the last fireball to destroy himself in a blaze of glory, as befit a devoted servant of Alfred.
HUN-HAT was defeated soundly, in a stupid haze, with Eilirilia unharmed as a bonus, by Alfred, all from the comfort of his own home.