Even ignoring the Serravelli clickbait statement, I wonder how much of an actual difference it will make between rental Hanifin and re-signed Hanifin.
As a rental, he is likely to get a 1st round pick, a top (not franchise-level of course, but one of the best prospects in an organization) + roster player coming the other way. That's basically the minimum. He should probably get a bit more as a rental. What does a re-signed Hanifin look like? An extra 1st round pick? Probably not. Maybe another 2nd? A 2nd and another good (b or c) type of prospect? I don't know.
Hanifin is a very good #2 minute-muncher who is very durable. Moves the puck exceptionally well, skates at an elite level, has great size and reach, and he regularly plays against the top players. He is only 27, and still getting better (believe it or not). That's why the Flames wanted to re-sign him rather than trade him (and I agree). He wants to go, so that's ok too - whether as a rental or a re-sign, Flames should do well in this trade.
I know there is speculation that it is only a few teams that he is willing to re-sign to. He holds an 8 team NTC. I imagine that all the Canadian teams are on it. Then add Buffalo (most likely) since Eichel is a close friend. Maybe Arizona since everyone has question marks with that arena, as well as questions about where they might end up moving to. That's 8 teams already. The NTC is basically meaningless during this trade deadline - though I guess it does depend on when he had to turn it in.
He will go to the highest bidder, whether that's a team that is looking at him as a rental only, or interested in re-signing him. Of course the re-signing team should be more of a return, but with Hanifin's camp saying where he is willing to re-sign or not, it will lower that market closer to the pure rental market, but it should still be a great market for the best defencemen available.