I don't think minor field repairs to the blade tip will void your warranty (not in practice anyway). I've seen much worse sent to Leatherman and they fixed/replaced it without a hassle.

Obvious, unreasonable abuse may be another matter -- such as burning the blades on a high-speed grinder and then demanding a replacement. They may well forgive you the first time, even though they're not obligated to.

I don't know if Leatherman tracks returns; they probably do. If you abuse tools outrageously, and constantly demand warranty service, you may get a less friendly reception over time. That's seems only fair (to me).

I never lend out anything (tools, money, etc) that I can't afford to live without if I don't get it back or it gets damaged.

Consequently, of course, I lend out very few items.

I don't see why reshaping the blade would void the warranty. Sharpen it enough over the years and you've reshaped it. Besides, those tips are so pointy that it's pretty easy to break off 1/8".

Purchase a new wave..

Hand him the one he damaged, along with the receipt for the new one..

Tell him that is what he owes you, period.

He owes you that. He bungled up your piece of kit, accept nothing less than a full replacement.