What will happen to Ethereum proof of work if asic miners are banished? Will the mining profitability reduce marginally or it won't affect the ROI? Are higher Hashrates better or not? Wil it affect Ethereum value ?
Do you like to fantasize?
That will not happen. Ethereum wants to quickly switch to the new POS algorithm and they will not change the current algorithm for mining.
I can't see any sign of quick switching to POS any sooner, why the EIP 1559 plan if PoS algorithm is already around the corner? I don't see that happening at any time, PoW algorithm is a big part of why Ethereum comes this far today, vitalik won't want to risk that