Sadly this will hurt Jet2 more than most because they own their aircraft and the value of classic 737's in the UK market will fall through the floor, most of bmibaby's fleet is up for renewal in the next 3 years (if the're still around)
I think that is should be calculated on the efficiencies of the aircraft. I also agree with you that it does some harm to Jet2, a great airline serving the community and the benefits it has brought to Leeds and Blackpool in particular has been fantastic.
If BMIbaby are here in three years then they will be here for the long haul and they have one of the largest players in the industry behind them...