I don't understand why it will stop working after some time.
If you're replacing the logic board, which has the faulty chip, why would it fail again by having a completely new logic board?
Same board, same chip, same solder, worse still old boards heated up until the dGPU functions again, which is simply BS. I work in the energy industry and we determined that refurbished boards are 7-10 more likely to failure, I am talking about boards that cost 10`s K USD, produced in low volume with Mil Spec components, and re-worked by highly qualified technicians. Not a mass produced consumer product, heated up by with a heat gun till it passes a minimal function test, Apple is just screwing you right now if your 2011 MBP fails due to dGPU.
Apple`s refurbished Logic Board`s are notoriously known to fail prematurely, hence the very limited warrantee of 90 days. If the boards had new GPU`s you would expect a couple of years use, not a couple of months. My advice is stay clear of MBP`s with dGPU. Hence Class action pending, equally no doubt same as the 8600GT fiasco Apple will only offer to extend the warranty on the afflicted MBP`s offering same poor quality Logic Boards or worse refurbished garbage...
Q-6