The octane rating of fuels in the USA is fairly standardized, a majority of gasoline cars require a minimum of 87 octane (on the US measurement system) and some even require or recommend a minimum of 91 octane. These requirements are usually for emissions and warranty/reliability reasons, but in some higher performance vehicles (which are a small subset) it's also for performance reasons. Using ethanol in a gasoline blend boosts the octane, so if ethanol is removed then something else will need to be used in its place. You can't just substitute gasoline in place of the ethanol with no other changes.
Ethanol has many downsides, especially with attracting water into the fuel, but it does have its benefits, too.
The octane rating of your fuel does not in any way affect the emissions of your car[0]. You should use whatever octane-rated fuel that your manufacturer recommends. Using a higher-rated fuel will not confer any additional benefits whatsoever onto your car.
Ethanol has many downsides, especially with attracting water into the fuel, but it does have its benefits, too.