There is no need to make decisions on something that's not been finalized or launched yet, I don't believe gpu miners can lose out even if Ethereum POW algorithm stop and go to POS.

1. There will always be a new coin that will be more profitable to mine as the mining hashrate from Ethereum will be moved to other coin

2. Even if the worst happens miners who can't mine other coins can still sell their gpu on online stores to gamers and graphic designers, you can't lose out completely