If you get a job with Ryanair as opposed to being a contractor the chances of being compulsory rebased are negligible unless you join as an F/O and then upgrade to commander - even then, when there is a vacancy you will be allowed to return.
At a meeting with a bunch of potential new guys, someone asked Michael O'Leary about this clause and he said it was to cover unforeseen events, suchlike as if a terrorist nuked Stansted and the whole base had to be moved !
A lot of rubbish is written on this forum but if you just get on with the job and look at the positive things you are flying new, well maintained aeroplanes to many destinations with interesting colleagues, getting well paid with a roster that allows you to plan your life and getting home in your own bed every night.