A freind of mine wants to coat a 1911 slide and is thinking of using Gunkote bake on finish and am wondering if the heat can damage the night sites
What do you guys think?.

I think you should take the sights out first.

It would be best if you were to remove the sights. If that is not an option, then depending on the manufacturer you should be okay. I bake mine a little lower than the recommended 325. I think you can achieve full cure at as little as 275*f
and as a little as 45 Min.

Spray a piece of scrap, then after curing at 275 for 45 Min abuse the crap out of it and see if it holds up to your expected level of abuse. Don't use something bulky that will act as a heat sink like an anvil or something. Also, even though it is scrap, prep it properly so you get as close to an apples-apples comparison as you can.

Remove the sights prior to refinishing. Tritium tubes inside of the sights will not tolerate high temps for extended times required to cure a thermal coating. Most of the coating manugfacturers sell an ambient version of their thermal coatings.