How many of these have been undone?
Kirk - Shatnerverse
Spock - TSFS
Scotty - Same episode as death
McCoy - Same episode as death
Data - Just last week,
Yar - Yesterday's Enterprise
O'Brien - Same episode as death
Dax - Jadzia no. Symbiont didn't die so no resurrection.
Janeway - Last month
Trip - Appaently didn't really die, was all a trick.
Honestly, I'm not sure I'd count something like "Shore Leave" or "The Changeling" where a lead character's "death" is undone by the end of the very same episode. Those are just blips to generate a bit of temporary excitement in the middle of the story; I doubt that anybody watching "Shore Leave" really thought that the show had killed off McCoy for good. Heck, he was back and flirting with alien showgirls before the body was cold . . . .
Dramatically, that's different from something like Yar's death, who came back after being dead for years.
Or even Spock, whose "death" was treated as a big deal that required a whole new movie (filmed a few years later) to undo.