It's a real shame that you got seen off with that motor. It's not recoverable and the cost of a replacement piston/liner/button/rod set is very high on novarossi's. To be honest it'll probably run if you dremeled the sharp edges away and checked the piston for any serious scoring or damage.

If it's ok after you've done the above clean it up well and rebuild it. Try it out and if it runs well it runs but it will no way make max power. If it doesn't run then you've lost nothing in trying and the only option would be to replace the piston/liner. Alternatively buy a new engine of the same family and use this one as spares....