I'll say it again, because some of the gossip in here defies logic...
Why would Jet2 run from LBA - their main base - and focus their efforts elsewhere? FR has 34 bases and that figure will grow. If Jet2 focus their efforts elsewhere, Ryanair will just go there in bigger numbers too.
Jet2 will fight Ryanair hand-to-hand at Leeds, some things will change, routes will be cut and both airlines will bend and wriggle etc etc, but ultimately they will just co-exist.
If Jet2 don't have an appetite for fighting Ryanair in their established stronghold, then they can't hope to compete with the likes of Ryanair or others elsewhere. It's this reason why Jet2 aren't about to crumble and retreat from running services out of LBA. Yes, they may strengthen their offering from elsewhere, but they know full well that Ryanair are omni-present wherever they go in the UK, so the two airlines just have to fight it out and carve their own markets, which will probably see Jet2 expanding further into holidays and charters while maintaining a strong lo-co offering too.
The two airlines will simply have a hostile-ish co-existence at LBA. That's for sure.