Personally, I think its more likely that the airline will intergrate the operations of the no-frills airlines back into the mainline, holiday carriers.
Hapagfly & Thomsonfly (BY) are both feeling the bite of the no-frills carriers, and rather than doing the typical knee-jerk reaction of launching a "me too" carrier, they are both beginning to offer seat-only flights on their holiday routes, and need to being having a cost structure, schedule (more than once weekly) & advertising to match their new no-frills rivals.
HLX & Thomsonfly (TOM) only distract the public away from the main brand, and whilst it does mean some pax are clawed back from flying with another LCC, these passengers really ought to be flying with the mainline carrier.
As has already been mentioned, little would be lost through merging the airlines back into mainline. HLX & Thomsonfly lease their aircraft & crews from the mainline carriers (HLX also get six Boeing 737-700s & flight deck crews from Germania - those 73Gs previously being used on thinner TUI routes in Germany/Austria) so these aircraft could come back to the charter fleet, and thus offer greater flexibility in the number of weekly flights & capacity available.