I'd say 8 years, 80 million sounds right. The Isles are a team built to be good for that tenure, so I don't think he'll want to leave, but I doubt he leaves money on the table like the last deal.
That said, it will be fun watching the Toronto media dream about UFA scenarios. The only thing that might give it validity is if guys like Nylander and Marner progress quicker than expected (won't even mention Matthews because the kid already looks like a legit top line player and the season hasn't even started). If those kids progress quickly, maybe JT looks at returning to the Isles vs going home to the Leafs and says, "I can play with Ladd and Bailey and have Ryan Strome as my 2C to (hopefully) draw some attention away from me, OR I could land a bigger pay day (including much larger endorsement opportunities) and play in front of family and friends, with a winger like Marner or Nylander and Matthews as my 2C to draw some of the tough match ups."
It's unlikely, but it's not out of the realm of possibility. Still though, JT kind of seems like the type to play for one team his whole career.