I can't see Ryanair removing its based aircraft from Belfast let alone pulling out, with or without Easyjet to compete with.
See, it depends on your interpretation of what a base is. I think a base is merely where they park their aircraft overnight, literally where the aircraft are based. It certainly doesn't mean that the airport is more important to Ryanair, after all non-base Derry and Knock have more routes than base airport Belfast; there are hardly any bases in France despite some airports having up to 20 routes. So in that regard there would be no problem having two bases in Northern Ireland: its just where they park the planes.
I think a new base at LDY is inevitable. That has to be what all the apron works were about. Ryanair could have continued to operate with the existing apron but with an extended runway.