I'll laugh pretty hard if Norris don't live up to the hype surrounding him, but that OT aside, the best thing that Mclaren has to bargain with Alonso is something out of their hands. In the end, it all comes down to how good that Renault PU will be next year. I wouldn't hold my breath. In four years of this regulation, Renault was always massively inferior to Mercedes and I don't think this will be miraculously/magically solved.
That being said, if Mclaren comes up with a really good car, like the Red Bull, they will be able to overcome the PU deficit on a few tracks and fight for wins(as RB was the fastest car on Suzuka's race, faster than Mercedes on Sepang's race, faster than Ferrari on Monza, and overall faster than Mercedes on places like SIngapore, Hungary and Monaco.....).
Mclaren's car is already quite good,
it's cornering speeds are pretty much on par with Mercedes, they can't drop the ball, though, and must built on this.