Oh man, my grasp of late season continuity is shaky, to say the least (to be fair, so was Chris Carter's). All I remember about the S7 premiere is the ultra-shmoopy "you're my touchstone" ending (I'm a sucker for shmoop, so I love that scene), and Mulder in the terrible old age make-up dreaming about the alien invasion, with dream!Scully coming in and metaphorically kicking his ass to wake up. I can't remember if Mulder going insane is ever referenced again, but I do know that later on, I think in S8, ~things going on inside Mulder's brain~ (being purposely vague to avoid spoilers) will come up that might be related.