No idea on what kind of egg it might be(that kind of stuff had never interrested me.. I'm more of a parrot person), but if you do find that the mother dies, it'd be best to hand the egg/baby over to a wildlife sanctuary or something similar.
Raising birds take alot of time. When first hatched, most birds need to be fed every 2-3 hours if I'm not mistaken(atleast thats how most parrots are). You also have to make sure you don't give too much, or too little. Raising a bird from a tiny baby is so dangerous if you don't have someone showing you hands on. A mistake could be crucial and a death could easily happen.
I know Argranade has experiance with helping wild birds, maybe she'll see this thread and be able to help you out much more than I could.
Good luck in whatever happens! =]