I have never regretted leaving Ryanair for a second. And never missed Ryanair since I left. I still know many people in Ryanair of which most want to get out. None have come across anyone who got hired back. And lets face it, you have to be totally desperate or completely miserable and insane if you go back to this bunch. Nothing ever got better in Ryanair, so why go back? I did hear of people receiving a phone call from Dublin asking if they wanted to come back, but all I know or heard of said big fat no. So would I. I think I might honestly rather get out of aviation than fly again for this bunch.
And in context with 'The grass isn't always greener'; well, there seems to be more actual grass outside Ryanair, with Dublin in this case being more of a desert than for example the Middle East.