Lips is everywhere, you just gotta know where to look. Lol. He's in a background monitor of the Jim Henson Hour below Zoot, maybe showing Zoot's the better musician? Who knows, maybe Lips will be back for this movie. He's appeared in Muppets take Manhattan, GMC, Muppet Xmas Carol, Muppet Family Christmas, and Muppets go to Disney.
I think Lips was replaced abit by Clifford in MGWDW, as Kevin Clash, who was on and off preforming Elmo at the time, didn't really have any other character, besides Leon, who wouldn't really fit the Muppet MAIN group.
Anyways... Dr.Teeth and Janice interacted twice, not counting the Muppet Show episode.
Dr.Teeth: EXTERIOR DESERT NIGHT, we knew right where you were.
Janice: Lyke, can you get behind it?
Janice: With RUUUL gewd music and organic refreshments...
Dr.Teeth: It'll be so fine, laid back, mellow and prophitable.
And in Muppet Caper.
Janice: Wait till I tell the guys in the band!
Zoot: Tell us what!
Floyd: Yeah, whats going down?
Janice: Kermit is going on a date with lady holiday!
Dr.Teeth: LADY HOLIDAY! AAAWRIGHT!