I believe the debate can probably be decided by 3 things. In reverse order.
3.) Your level of experience
2.) Whether your level of experience is in an area which Ryanair require you.
1.) Who you know that is very senior in the company and will therefore support your case.
I only konw a few guys that have returned to Ryanair, however they were experienced, previously long serving employees. Undoubtably they knew a few peeps who would ease their re-entry process. I know a number of not so experienced chaps who left because they believed the 'grass was greener.' It wasn't and FR told them to **** off.