The SPOILERS say that SG-1 will likely become a 3-person team with Carter in command. I wish that TPTB would consider adding a new, young Lieutenant to the team, so we can watch their development throughout the season. It could be the catalyst to making Stargate SG-1 more of a fluid show, allowing characters come and go, without having to cancel it.
This formula works well with shows like "Law & Order" and "ER" and I see no reason why it couldn't work for SG-1. In real life military teams change...there's no reason to believe they can't make that work for SG-1. It worked with Jonas.
Of course we'll miss the old characters, but, assuming they're not killed off, there is hope to see them again. If the show is cancelled, we never will. I doubt it will happen, so all our hope now lies with Atlantis.