As for as I know, they are still doing a lot of shows without an accordion. I know for certain that Jesse Lege has played a couple of shows with them, as well as recorded with them. Jo-EL Sonnier has played a show with them and will be their special guest at JazzFest, this year.
I've been wondering about that, too. I always liked the way that Jimmy Breaux played the accordion, even if in an understated way with Beausoleil. I thought that it might be difficult finding another accordion player who would accept the role that Jimmy Breaux played with the band.
From some things that I have heard, I think that Michael, David and Mitch may all be sharing Jimmy's role. I heard that Mitch learned to play the accordion from Joe Hall. In other words, I'm not sure that they are going to add a full-time accordion player. It will be interesting to see how that works out.