Had it happen to me last year really bad. Lost about 1/4 of my crop to a fierce storm. If the branch is still attached to the stem at all, and not completely broken off, then just make a splint and tie it up and it will be fine. I've even heard of people using duct tape to reattach it to the stem with good results. I just grab a small stick and wrap it to the stem with pvc tape ( that green plastic tape they sell at garden supply places) making a splint.
I would not leave it touching the ground though, as its an invitatin to bugs and such, plus getting dirt into the buds sucks.