I'd run it back one more time.
I don't WANT to do that, as I don't find this core (Matthews) all that likeable, but that is the best shot to win a cup right now. This team/core is 'aging out'. Almost every cup winner in the past decade (or more) has had one or more of their top star players no more than 26 years old:
-Florida last year: Tkachuk 26, Barkov 28, Bennett 27
-Vegas 2 years ago: Eichel 26
-Colorado: McKinnon 26, Makar 23
-Tampa: Kucherov 27, Point 25
-Tampa (before that) Kucherov 26, Point 24
-St. Louis: Schenn 27, O'Rielly 28, Tarasenko 27
-Washington: Kuznetsov 26, Tom Wilson 24 (Ovi was already 32, this may be the exception)
Crosby won his cups at 29, 28, and 21.
Patrick Kane won his at 26, 24, and 21.
Kopitar won his at 26 and 24.
Mario Lemiuex won his last ones at 26 and 27.
Gretzky's last one in Edm came at 27 (27, 26, 24, 23)
My point? You CAN be a very good player in your later 20's and into your 30's, but to be great and carry a team through the playoffs all the way to the cup, you USUALLY (almost always) need one of your stars to be in their early to mid 20s. Matthews may still be at his 'peak' in terms of talent, but he's not getting better, and injuries and wear-and-tear are starting to take a toll.
Next year at this time, Matthews will be 28, Nylander 30, Tavares 35, and Marner 29. I'd give them one more shot next year, if they don't do it next year, this window is closed after that. Not closed to being a very good team, but closed to winning a cup. One more year.