Runaway 2 stroke engine

Last year I had put my 05 rm125 back together after sitting for a long time and took it out for a spin for about 30 minutes until the engine ran away on me. Kicked the bike into gear and held the brake and stalled the engine. So anyways my dumb ass didn't put any coolant in the bike when I finished putting it back together, so clearly it had over heated. The bike has sat since and I've just started working on it again. I never even tried to start it later on after it cooled down, but before I finish it up and go to start it again I'm curious what I should look for and what you guys think the bike overheating would do to cause it to run away. Could that have blown a crank seal possibly? I pulled the reed valves and they definetly need to be replaced so maybe that has something to do with it as well? Some advice would be much appreciated, thanks!