I was ready to let him hit free agency as a pure rental at the deadline. That grew to straddling a fence closer to the start of the playoffs. After game four, I'm convinced they need him for the immediate future.
They can largely reinvent their entire top-four next season by keeping Smith, IMO. Shattenkirk is just a matter of time in my eyes (as is a Girardi buyout), so if they manage to extend Smith to a reasonable deal—say $10M over three years, give or take on dollars—they can likely go into next season with a completely mobile, completely interchangeable top-four of McDonagh, Shattenkirk, Skjei, and Smith.