Yes, McFadden left for a bit to have a baby. And most of us TNGers hated it when Pollaski was on the show. Not only was the character a real stick in the mud curmudgeon type, but she also dissed Data pretty early on in her run.
Scene was something like:
Dr. P. "Well, Data (pronounced DAHTA), I really don't see the point of doing a physical for a robot. So, I guess we're done here."
Data: "Excuse me doctor, but I am an android, and it is pronounced Data (DAYTA)."
Dr. P.: "DAHTA, DAYTA - What's the difference?"
Data: "One is my name...the other is not."
Anyway, without Gates McFadden the show also dropped in babe quotient, what with Denise Crosby having been killed off (now, that Character, Tasha Yar, was the one with Rodenberry's interference...he wanted her more butch than Crosby, and Crosby was afraid of getting typecast forever like TOS stars at the time were sufferring...so she left. Now she is still typecast, as a former Star Trek star who can be seen taking her clothes off in such gems as "Red Shoe Diaries 92: This time we drop all pretense and just show you porn" and schlock like that.)
So we were all pretty happy when Dr. Crusher came back AND Wesley left for the Academy. Good times.
I sure hope JMS gets a chance to do Star Trek, though, that would be awesome!