Yes, and you weren't very convicing.
The Wizard 20 is informed that his task is to defeat the sorcerer in vague terms. [This is necessary for the whole setup to work, if not the fight can't happen because both parties don't know about each other and there is very few reason to imagine someone will spend a single spell slot to off a meaningless Holed Up Target...
So he can be Scryed as a PERSON, but based on only second hand information, it works only if the Sorcerer fails a WIS saving throw with a +5 bonus. +0 (no ability bonus, no proficiency) +5 +2d4 (average 5 if you sepnd your favored by the god power on the first saving throws of the day... can we assume it's an established fact?) will give +10, against the wizard DC at least 19 if build with any modicum of sens)... That's one in two chances, each day, to fail. Really quickly, the scrying beacon will appear near the sorcerer. As he has no means of transportation, he is very close of his "fortress". With repeated attempt, the wizard will scry right at the moment the sorcerer is near his fortress and will have seen it...
It is of no importance since it was established later that the Sorcerer NEVER EVER leaves his Private Sanctum. So yes, the wizard can't scry him, but it has no relation with the ability to see invisible things and be clearly related with the sorcerer never leaving his private basement, doesn't it?
OK, so now the Sorcerer is hidden in his Demiplane, which he never leaves. I am really pitying the existence of this poor level 20 creature and I think the wizard will make extra effort to kill him because it's the charitable thing to do in the name of Ilmater... Is is established that the Sorcerer never interacts with the Prime material plane and just stay in his demiplane-borne fortress?
Could someone who is not the OP enlighten me on the Summon Retriever spell ? I'd prefer the exact spell description because some wording errors have already popped in this thread.