7/8 x daily at LTN isn't sustainable, fact. There will not be that level of service in 2 years time, probably sooner.
What will probably play out is FR move the service to STN, frequency will probably remain because they are also fighting Norwegian at LGW. Frequency at LTN by EZY will reduce to 2x daily, then 1x daily or dropped altogether. SEN would work I feel, but only if EZY attempt to stay in the market with the ease of SEN as their USP.
There are of course other externalities that could affect things, such as FR having such a spat with the unions in Denmark it is impossible for them to continue.