well there are a couple of things you can do.
1. you could try to retap the pedal crank
2. you could drill it out and put a helicoil in
3. if it's the side of the puch pedal crank that is just the arm, and not the entire shaft and sprocket assembly, just replace the crank arm also.
4. if none of these apply, and it's the side with the pedal shaft, then you'd have to pay around 50 dollars for a new one, so I'd say go ahead with the welding.