This is why I say Nylander might not want to sign before Marner and if he keeps outplaying Marner the way he has been, I could see it playing out like this. He's held out for months before so I don't think he as any issue with becoming an UFA, I think it's quite likely that this happens. And everyone should understand that UFA's get overpaid, that's just the way it is. So if his true worth is 10, there's no point in complaining about having to pay him more, you either pay him more or you might lose him for nothing, that's just the way it works.
It might be the case that Nylander would be willing to sign for something like 10.5 today, if it wasn't for the possibility that they give Marner something like 12 later and I can't really blame him. So he waits until the summer, becomes UFA and no matter what Leafs offer, he says get back to me once the Marner contract is done, I want to see what his cap hit is first and in the mean time, he can sit back and consider all the money other teams will be throwing at him. Someone will probably offer him at least 12x7, so he'll be in no rush to take 10 (or even 11) from the Leafs, especially not when there's the possibility of them giving Marner more later. And if making max money is his top priority, then he's gone because the Leafs will be unwilling to match the top offer.
The best course of action might be for the Leafs to decide that they are willing to offer Marner and Nylander both 11, and tell them both that right away. If they can convince Nylander that they mean it, than he might be willing to sign now. But if Nylander doesn't think he can take Tre at his word, they might have to go public with it to convince Nylander that they really mean it but that's something they won't want to do so the only option then might be to just wait until the summer. Either way, they're in a tough spot with Nylander, no doubt about it.
Not sure why people keep ignoring the fact that Marner has that pesky NMC. Might just have to let him walk if it comes to that.