I think as long as their "honeymoon phase" wears off, they are committed to iCarly, don't leave Carly out of things, don't drag Carly into arguments anymore, and be themselves(not OOC), then I think she will be fine. Wow, it kind of sounds like a lot of conditions. I don't really like couples if the other characters(especially the main character) finds the couple annoying. Basically if Carly is unhappy, then I will be unhappy. I think Carly will be upset, but they work out their issues in the end. She seemed supportive in iLMM, she's a good friend and wants them to be happy(lol I should take a shot every time I say this or something). So as long as Sam/Freddie don't cause problems, which they probably won't after the arc, Carly should be okay with it.

Lilly/Oliver was always overly affectionate when Miley gagged/was annoyed for them, at least from what I saw. I skipped a lot of episodes. She was still supportive of them together and liked them together when they acted the way they used to. But yeah, after the arc their relationship will probably stay the same with some small interactions.