I usually have the answers to most TC questions, but I don't for this one.
Would it have lasted as long?

The Ropers leaving was planned. Chrissy's wasn't.
I'm glad Suzanne Somers had the contract dispute, because Chrissy was ruining TC for me.

In later seasons we see a change in the group dynamic because they finally left the apartment and got a change of scenery here and there. I think the same would've happened if Chrissy stayed. I'd like to think if Suzanne had stayed she would've had a reverse Flowers for Algernon effect....after her brief period of utter idiocy in seasons 3 and 4, she would slowly grow smart again. Maybe they would've had her change jobs for the sake of more scenery options.

I like Mr. Furley but the Ropers were my favorite landlords. They gave the show a cozy family feeling, whereas Furley was more of a kooky friend. However, could the Ropers have continued making the same sex jokes for another five years? I don't know. I can't think of anything that would change about their situation to keep it fresh.