My ideas:
Atlantis: Now that Carter is there, kill off Weaver and let Carter take over.
New Series: SGC decodes use of the 9th chevron, teams start exploring other time/dimentions or alternate realities.
Ohhh yeah. The could call it......wait for it........."Sliders".
Just joshin' ya.
That could be a real good set of story lines. Perhaps even culminating with a face to face with The Ascended Ones. They've been cruisin' for a bruisin' for some time now.
"Weaver"?
I think you mean "Weir". I disagree. There was a crossover episode with all the characters from both shows awhile back, and it was very good--no need to kill off any more main characters on Atlantis.
Isn't that "ER"?