Curious, I was not aware that Disintergrate didn't function, did this change from 3.0? The example I was thinking off took place using that version of the Archmage. Assume that the Archmage also has reactive counterspell and master of counterspell (sooner because he doesn't have to get through Red Wizard levels to get it)
Our epic FR DM is not exactly the best at plot development or preparation, but when it comes to designing retribution for such groups she does a fairly good job. Though perhaps I am not describing the situation clearly. We killed the Red Wizards who were involved in selling a series of particularly nasty drugs into Om and other places along that coast. Now we are currently investigate similar happenings in Waterdeep. I doubt Szass Tam is that concerned with the drug trade to invoke his masters aid due to losses on an admittedly large but not crippling scale.
Admittedly that game has slowly become extremely munchkin, due to in part the rolling randomly for treasure. Let it be said I consider that a mistake. But any DM can kill any part at any time. The question is what makes for a fun, interesting, and realistic (I used the term loosely) game. What I am flabbergased about is the fact that you honestly think that the PCs, even Epic PCs, are the center of the universe.
1. Larloch honestly doesn't care much about what goes on outside his lab, they said as much in many seperate sources. Before Szass Tam, anyone who bothered him would be horribled killed. I don't debate the fact that he could right now, horrificly maim and slowly kill every member of our party by himself. I debate the fact that we are even at the forefront of his mind. More likely his attention is resting on the return of the Shade Enclave and their artifacts and mythalar. If he was honestly going to toss epic undead at people why has he never done so in any FR source? Why do Halaster, Shade and Cloth still possess Nether Artifacts?
2. Admittedly Szass Tam could be incredibly pissed about the whole affair, and could organize a Red Wizard strike team that likely could wait in the shadows and pick us off left, right, and center. But in order to do that, he has to bend a group high level wizards to his will long enough to convince them that we are a huge threat that must be eliminated, no matter the fact that they would have to weaken their position to make the strike. Either this is easy or extremely difficult. If it is easy, why hasn't he conquered the realms yet? Right now we could stand our own with most of the power players, (the Chosen of Mystra, Most of the sword kindoms, and most of elven lords now). If he could basicly destroy any of them, why does he tolerate the Sisters continued attacks upon his holdings? Indeed, why has he not simply destroyed them now, if his power is so great?
3. Consequences and Reprisals. Right now, we are affiliated with a noble house which is nobility in Waterdeep and in Om (one of the characters is the head of the family). The estate were we dwell has many interesting magical properties, woven in times of paranoia. The first of which is the fact that no one but ourselves may teleport into the estate. The second is the wards against scrying that are placed through out the mansion itself and any attempt to teleport in lands one in a room a locked room 81 square feet total. The room is covered by an permanent antimagic field as well having no food or water. Outside the mansion, their are several golems and Clockwork Dragons guarding the against intruders.
Outside of the mansions and grounds proper is a series of two temples. One to Baccuss, which leads to the wine orcherd and houses many clerics to that deity. The other is a temple to Bahamut, and we regularly have good dragon worshipers arriving there.
Again I don't debate that he could, with sufficent effort destroy us utterly, but the consequences of such an action would be dire. First, it couldn't be quiet, that level of conflict would be sensed by massive numbers of people. And assuming they manage to get us all. They still have to deal with consequences of having angered (alot) of Gods that are hardly slouches, including Baccus, Bahamut, Timara, and a host of other dieties whom we have done good works for. As well as the fact that they have essentenially committed an act of war against both Om and Waterdeep by assassinating an important noble and laying waste to his house.
Either the PCs are important enough to matter to both Good and evil alike, making their deaths the beginning of a multiplanar




storm the likes of which Toril has never seen. Or they are below the extreme notice of both.
In Summary, I honestly believe that Thay as a nation is quite as powerful as you would contend, realitive to the world in which they live. I also contend that any party that would be doing enough lasting damage to warrant the type of response that you are suggesting would likely be valuable enough to others to protect.