You can try to work out the details to save money, but unless the work is free, a comparison of the cost of the work, and the cost of a slide, new or used, would be added on top of that if it doesnt work out. My apologies if I'm missing the mark, but trying to cheap out on an important part isnt always real economy.
A couple of your comments come to mind,
I'm inquiring mostly about potential heat damage.
Other mention this, and you dont seem to want to give it much credence. Call Glock and ask, though they have looked at it and told you it will be OK as is.
As above, you ask opinions, and dont like the answers. If it was your fault, and they way it is bothers you, you can have questionable work done, or just step up to the plate and deal with it by buying a new or used replacement part. Glocks arent 1911's. 1911 breech faces dont chip out, glocks sometimes do. I'd seriously be hesitant to have welding done on a glock breech face. Its your gun, however, and you are free to do whatever you want with it. I'd not feel good about ever selling it in that condition even if it seems to work in the near term. You may choose never to sell it, but if you drop dead, nobody else may know about it when it gets sold off with your worldly possessions.
So how does Glock install the rectangular firing pin hole in the slide? Is it broached? EDM cut?
I dont know how they form the firing pin channel, but they'll sell you a perfectly good example for likely a pretty reasonable price, or a good used one can likely be had for a fair bit less.
