None of the support staff will be used in this story, Chewy, so there's absolutely no problem with you removing Grissom. The team is going to be in another dimension and completely out of contact with the world, so unless the support staff are seen in a separate thread which deals with what they do during the team's absence, there's absolutely no call to use them once the team has left.

You're free to write Grissom out of the picture "on panel" in the story, but it's really not necessary and I wouldn't recommend it since it hasn't anything to do with the story. We'll just make sure not to refer to him in the present tense.

In effect he's already "written out" since he hasn't been a member of the team since issue #13. It's best if you write him leaving the support staff in your story rather than the team story, since we're trying to get away from this kind of "off-topic" thing in the main stories.