If this season marks the end of McLaren's engine partnership with Honda, then switching to Renault engines would leave the team no place to hide in 2018.
Chassis-wise, it would be compared directly to Red Bull, and the works Renault team; and if Fernando Alonso stays on alongside Stoffel Vandoorne, then McLaren would be, driver-wise, able to go up against Max Verstappen and Daniel Ricciardo. That means no excuses - it's put up or shut up.
The entire situation is a little sad for Honda. It came back to Formula 1 with the best of intentions and by allying itself with McLaren was very much there to be shot at. Honda could have spent a couple of years learning the ropes with a smaller team, but it didn't and that has led to a big cost financially and in terms of credibility.