It won't happen but if BTC did change it's PoW then no the current value could not support all the hashing power there is just not enough value there you will possibly find miners refusing to mine really low value transactions antpool and f2pool was doing that a bit back on BTC
f2pool even tweeted out that if you want them to mine your transaction then you need to pay a higher fee
A similar thing will most likely happen the miners may refuse any transaction below something like 10sat/B
You would probably find many miners quit and bitmain unable to sell new mining equipment
So never say never https://twitter.com/CobraBitcoin/status/967237696379813888. Sadly enough is it desperation signs Or another high level fud? But one thing for sure that cannot be called Bitcoin anymore.
If bitcoin was to change the PoW algorithm it would still be Bitcoin eventually it may have to happen as quantum computing starts to become a reality but this will probably be many many years away and likely not in our lifetime