Immediately after I helped reassemble my friends camaro's 4L80E transmission, he filled it up... after warming up, it showed low on the dip and in the dark, he accidentally put about a quart of synth motor oil down the tube into the tranny.

What will this do, especially since he doesn't have any intention of dropping the pan and refilling correctly?

I don't think it will hurt a thing. A friend once put straight motor oil in a trans that started leaking bad out front seal, he was on a trip and that's all he had. It worked just fine. One quart out of 15 won't hurt a thing, in fact, it will probably add a little more lubricity to the atf.

I don't know but for sure I'd drop the pan and change everything out to correct fluid. Cheaper to do that than take a chance on doing a major overhaul again.

I dunno how much it would hurt, but may not be an issue. I use grape juice as an assembly lubricant when I build transmissions... works much beetter then transgel.