This article is from the NYPD Blue FAQ, by Dave Chapman, Alan Sepinwall and Jeff Knapp with numerous contributions by others.
There's not a lot you can write about the squad secretary, and
once Greg and Donna broke up, Gail's role on the show shrank
so much that sometimes weeks would go by without her saying
anything. Fox offered her own sitcom -- she made a pilot, but
it didn't get picked up -- and she decided it was time to move
on. She's been working in movies lately, most recently in
"That Old Feeling" with Bette Midler.
As for Upstairs John, Bill Brochtrup had taken the character
over to Steven Bochco's sitcom "Public Morals," which got
cancelled after only one week. Whether he'll return to "Blue"
remains to be seen, though both Brochtrup and David Milch have
expressed interest. Don't be surprised if he turns up on
Bochco and Milch's upcoming CBS cop drama "Brooklyn South."
So, for now, Gina Colon is the squad PAA.