If you're reasonably handy, you can replace the shingle yourself. I'm
sure you can find details on how to do it on the web. Or else hire
someone to do it. If the rest of the roof still has some life left in
it, just fixing this is cheap and easy. Either way, I wouldn't wait
to see if it leaks, unless you want the expense of repairing water
damage to ceilings, etc.