Ouch. thats a pretty hefty hit. have you kept the other bit that snapped off or has it completely dissapeared. if you still have the other end, i would(bearing in mind it wont look good but it might work) epoxy the nose back on, and then get a load of P38 filler, or maybe some solarflex, and basically dip the whole lot in, let it dry and then reshape using plenty of sanding paper. when you get down to a nice finish use very fine wet and dry sandpaper. this will keep it water tight and give you a nose.
now if you dont have the bit that broke off its more tricky. you could maybe reconstruct one out of balsa wood and glue it on. it depends how much you love your board, and whether or not you want lots of work to do. but the easiest thing to do i think without the nose, is to cut it off flat at an angle. / like that but much shallower, and then reconstruct a blasa wood nose and glue in place, and then use filler, or solarflex, or some other form of material. you could use epoxy resin with glass fibre.
im not a surfbaord repairer, but if it was mine this is what i would do with my board. other people may advise differently. some might say get a new board or get it professionally repaired, but these can cost a lot of money. i paid £50 just to get an FCS plug glassed in and for my board to be dried out. but he did a very good job i must say.
the choice is yours. things to consider are, time and cost, as well as how good you are with DIY materials and tools. it can be done, but it will take some time.
i hope this helps, and sorry for the very long message
Tj