I still worry about group situations too. I'm okay with maybe up to four people, if I know them well. After that...not so much.
However, I'd say go for it. I think they'll be very glad to have as many people show up at this event as possible.
If anyone does ask why you decided to come back after such a long absence, say something like "Well, I had a lot of stuff going on (work/working on your music/whatever) but decided that I wanted to start coming again."
Or something like that.
In actuality (don't take this the wrong way) probably no one's going to care--people come and go from groups all the time, for many reasons.
Let us know if you decide to go. If you decorate a T-shirt, take a photo of it if possible (maybe on a camera phone) and post it here.
Good luck.
_________________
The existence of the leader who is wise
is barely known to those he leads.
He acts without unnecessary speech,
so that the people say,
'It happened of its own accord.' -Tao Te Ching, Verse 17