split the cases and completely strip the engine, removing all the metal and shards and go along the cases with a magnet to get all the little shards, odds are there will be more damage than you first anticipated
only real way is to strip although once i did fill a crankcase with parafin and shake about then empty a few times till i was satisfied. but i wasnt even sure anything was in there lol
Get someone to press it out for you. Don't do it yourself if you intend to use the crank again. You will need to replace the crank bearings aswell.
With my rd125 I used a magnet to get big bits then filled with petrol and shock it around and drained a few times