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.
So POW and POS algorithm will both exists on Ethereum blockchain? Where did you get this information from or you just guess things out on your own without official announcement? Anyway I pray it will be so honestly it's what I hope for, POW algo need to keep existing on Ethereum blockchain