I'm sure EZY will agree retrospectively that they shouldn't have switched CPH from STN. It turned out to be what looked like a failed attempt to try and squeeze out slightly higher yields.
If EZY have ditched the route, it wouldn't surprise me now to see FR switch their CPH flights over to STN, perhaps not for S17 but possibly beyond that. As such I'd be surprised to see EZY reinstate STN-CPH.
I firmly believe what FR say in that any price war with them (and LTN-CPH is one of the hottest price wars we've seen between FR and EZY for quite a while), FR will always be the winner. They have the lowest cost base so they can afford to reduce fares further than anyone else.
Of course if the rumors going around that EZY will be night stopping in CPH then that's a very interesting and brave move in my view - but can't see it happening myself, and they already night-stop in CPH on the LGW route.