I think its a mistake of Jet2 to take on Ryanair becuase it all really comes down to price but we shall see.
I doubt GSM will completly be wiped off or Jet2 for that matter (though i doubt DUS will last). GSM are very Dominant of EDI-Spannish routes and are very well known in Scotland as a whole if they have trouble at EDI they would just make there GLA base larger.
You never know i believe if there was to be a merger of Jet2/GSM there could be a bit competition of FRs hands!