Can't help with dis-assembly / re-assembly of the instrument cluster since I haven't done that (yet), but I know how things like that go, and would suggest not going there when you're planning on leaving for a road trip this afternoon.
The bolt is probably pressed into the back half of the plastic housing of the cluster, unless there's a lock nut on the outside to hold it in place. You could try poking the end of the broken bolt to see if it's loose.
I would say don't worry about it until you get back, because it's probably not going anywhere (the bolt head or the cluster). Other than annoying you while you ride, it should be fine. Not like it's going to fall off.
There is a post on here somewhere (almost remember by who), where they shimmed the cluster mount bolts to remove some of that play. There were some pictures of a dis-assembled cluster on here, but now that I think about it, they were probably on the pre-crashed site.
Hmmmm..... maybe that is all the further they tighten and the slop is all the tighter its supposed to get without shimming. What good is mounting it into rubber if it can't even press into it for dampening? It behaved like it was all the further the nut would turn and it's such a small bolt it broke as soon as it turned the ratchet. They have some rivets in so I'll just button it and stuff some foam in the top.... enjoy my ride and worry about how the bolts are handled on the inside when I get back.