Imho, "as long as it's done well" fits my mark. As long as I feel sufficiently entertained by the stories and connected to the characters, I accept change and returns to SQ equally.
For example, I'm okay with TNG stories that feature Picard as an integral character after he resigns his commission, but I equally enjoy it if he stays in command - as long as it's well-written.
However, I'd rather not see a canon main character killed off, though I cannot justify it on an intellectual level. I still haven't gotten over Tasha's death. In spite of that, I'm not one to call for resurrection. Janeway's and Data's return were gratifying but I would've never complained anyway.
Bottom line is, I'm generally easily pleased and would go along with almost everything. Blow up Earth, if you want.