You take away Kirk, Spock, or McCoy you've got issues. You take away Picard or Data you move on.
I definitely think a TNG film series could have moved forward without Picard and Data, but it would have been a very different film series as neither Generations
or First Contact
would've turned out the same. Whether it would've been better or not is, of course, debatable.
I thought DC Comics did a bang up job of giving us good stories between The Search for Spock
and The Voyage Home
. Stories such as The Trouble with Bearclaw
, Maggie's World
and The Doomsday Bug
(which brought the comics back in line with the films) were compelling even with Spock being absent from the Enterprise
While I love those comic stories(except Bearclaw is a too over the top jerk who wouldn't have lasted a day in Starfleet) I'm not sure they're a good indication of how movies without Spock would have worked.