If Buffalo was to trade for Hellebuyck, I'd view it as similar to the Huberdeau situation last summer.
The only correct move is to commit to the guy for the last year of his contract and plan on losing him. If he comes to Buffalo and and has a solid year and has you in the playoffs, great; keep him for the season and then trade his UFA rights to recoup something (assuming he wants more than a 1 or 2 year deal). If he comes to Buffalo and the season goes poorly due to injuries or whatever, retain salary and flip him at the deadline for something juicy.
If you're set on signing the guy to a long-term contract, you're likely going to get burned.