First of all, pure AI-generated code is uncopyrightable now. Uncopyrightable code can't be under GPL.
Secondly, GPL can't "make your (proprietary) code disappear." Violating GPL is essentially just stealing code. One cannot distribute the version that includes stolen code. But they can remove the stolen part and replace it with their own code. Of course they still need to settle/pay for the previous infringement.
GPL simply can't affect the copyright status of rest of the codebase, because it's a license, not a contract. It cannot restrict the user's right further than the copyright laws.
Again, it's very common misunderstanding of GPL's "virality." It has been a several-decade long debate about whether GPL should be treated like a contract instead of a mere license, but there is no ruling giving it this special legal state (yet), at least in the US.
[0]: https://lwn.net/Articles/61292/ [1]: https://en.wikipedia.org/wiki/GNU_General_Public_License#Leg...
First of all, pure AI-generated code is uncopyrightable now. Uncopyrightable code can't be under GPL.
if AI generates something that is equal to existing code, then the license of that code applies. the AI generated product as a whole can't be copyrighted, but the portions that reproduce copyrighted code retain the original copyright.
they can remove the stolen part and replace it with their own code
sure, if they can do that, then they can distribute their code again. but until then they can't.