That't not how offer sheets work. If Nylander signs one, then the Leafs have something like a week to match the offer. They can't give him a different offer, it has to be a match of whatever he's offered. Also NO ONE IS GETTING AN OFFER SHEET!

If he's offer sheeted, they have to either match or let him go, they can't just sign a different deal.

I'm saying that Nylander has the offer sheet in hand, but not signed. He uses that leverage to get what he really wants and that's being a UFA in four years.
There has been reported offers sheets in the past, that players haven't signed for various reasons. One reason is the player does not want to tied down for seven years or he fears that he old team will match and doesn't want seven years with his current team.

I never said Nylander signs that offer sheet. He has it as leverage to get his four year contract. The $$$$ amount of offers sheets have risen considerable, it's getting to be a better hockey trade for teams to offer sheets than in the past. May not happen as you suggest though.