These sorts of "not that important" decisions... I flip a coin.
If you assign Heads to "going back to choir" and it lands on Tails, and your first gut feeling is disappointment, then you know you should go back.
I was also a member of a choir for many years, and made the very difficult decision to quit mine about 2 years ago now. I didn't really enjoy the conductors style/personality, and wasn't really feeling the music we were being given. It was becoming a chore and a "Oh, it's Tuesday, that's choir night..." Instead, of "Oh! Yes! Choir tonight!"
I agonized over the decision for ages. But once I quit, I thought of them maybe a couple of times, but truly didn't regret it for a moment.
In your case, I think I'd tell myself, "I'll go for one term, and then reassess." Like you, I had a choir buddy who stopped going the term before me, and it wasn't so fun then.
The way I see it, choirs of some shape or form will always be there, and I can always join one again if I feel the desire.