Cheap answer is always the best to try first
Strip the carb, sounds like it pulled some crap out of the bottom of the tank when you ran it dry.
"just a thought, check the tank vent, sometimes this is the problem. I had a new ski-doo, and it would run fine for a little while and die, would not start until it sat for a while. It finally siezed the motor and that's when we found the vent tube was kinked . caused a serious lean condition."
"I'd pull the plug when it won't start and look for spark. I've seen the reisitors corrode in the caps too."
In that order.
Old bike should really have fresh main seals, $20 for a flywheel puller, $20 seals. It dont cost a mint to ride old bikes just common sense & not throwing money away on guess's. Use the process of elimination on the cheaper fixes especially where you can get it to run. Should be a blast once you get it sorted, I sure wouldnt mind a 90's RMX250 myself