EDI has been operating 3 times weekly since the start of August and is going up to 4 weekly in October so I don’t think you will have to worry about going out via LHR. The timetable is only finalised until the end of the the summer schedule on 24 October.
It may be a case of once you book and the November schedule is uploaded that you may have to shift a day either side as flights are unlikely to be daily but I don’t foresee any issues of QR terminating EDI service for the winter season.