Conversion will not happen overnight and it is not intended to happen overnight. There will be a market for ICE Cars for 2-3 more decades probably.
I think Electric will win out simply because they perform better. If you gave me an ICE car and a BEV car for the same price, it is not even a contest as to which car to take. Factor in that BEV's are cheaper to buy and cheaper to operate and it's a no brainer that they will take market share. Ev's are too good and too far ahead for hydrogen or something else to catch up imo. Battery prices are dropping like a rock too, BEV's are just going to get cheaper.
Will there be some alternative fueled cars? Sure, just like there was BetaMax for a while.