A billion euros of cash is a decent cushion, so Ryanair will be flying for the foreseeable future.
But what will they do with all these new aeroplanes?
They could pick off competitors like cherries, if they saw fit. Take Leeds-Bradford. If FR moved in there on Jet2's routes, and flew everyone for free for a couple of months, Jet2 would probably suffer fatally. So FR would inherit a handful of routes with established client bases and use up half a dozen new 737-800s. It would cost a few million £, but whoever would challenge them after that?
Of course, they haven't implemented such a strategy, but they could afford to, and could destroy any competitor that didn't have their massive cash cushion. Not only that, they would be buying (stealing?) an established base fairly cheaply.
Just a thought.