Don’t think of it as seven years bad luck, think of it as an opportunity to be creative. If you are worried about the seven years of bad luck you can bury a piece in the garden and that will stop it. (so I have heard). Here are some ideas for broken mirrors, most of which I got from Fusing 101: Any and Everything You Wanted to know but Were Afraid to Ask.
This from Jane Wimbury. How sweet is that!
Another idea is to get Styrofoam balls and make garden balls. Or use an old bowling ball:
Frame the irregular shapes for eclectic mirrors:
Just put it back together roughly for a high interest look. Many of these ideas from dyi.
I can see this done with wine corks, as well!
Try your own designs – Good Luck!