Yeah, I think I heated mine with a torch to get it, I can't remember.
I'd think it can take a cheater bar worth of torque since it's a 3/8 NPT. If it's severely rusted on the inside though, it might shear off very easily. On my complete tear down, half my body bolts sheared off at the head even from just elbow torque because of the rust.
As BC59 said, you COULD always drill it and re-tap or try an EasyOut. Problem with easy outs is if you snap em off you're in a world of hurt.
The heat up method is nice because it expands the bolt, crushing the rust in the threads, and then you cool it and it shrinks back, helping get the rust unattached.
All in all, you've got different methods to try, but if the engine is still on the frame, I'd suggest working on that drain plug. I'd try a few soaks of PB or Kroil followed by light pressure on a cheater bar. If that doesn't work, try the blow torch and wax method. If that all fails, drill the dang thing.
