I talked about this pages ago, but the problem is that we don't have a point of reference for a similar deal.
The argument that Tavares won't want to weaken his new team is valid, but so is the desire to get that 8th year. $84m over 8 years is only $10.5m, it would take $12m over 7 to get that same amount of security.
Ultimately, Tavares isn't going to be agreeing terms with 3 or 4 teams and letting the Islanders play them off against each other. In this scenario, he'll pick a team and it will be on the Islanders to do the best they can. WPG 1st & Blais/Sanford? Maybe include Gunnarsson just to move some salary? It's a lot for a player who is days away from UFA, but you pull the trigger on it because it takes away all risk and massively improves the roster.