If you want to remain mediocre for longer, you give big/long-term contracts based on need rather than the talent of the player.
It doesn't seem like you really read my post. I specifically said, for the right price and term, I wouldn't mind seeing Nelson return.
And, maybe it wasn't clear, but if they could find a fair deal for player and team, I would be fine with Nelson as the 3C. With Barzal and a better 2C in place, Nelson could be a very strong 3C and better than mediocre.
The Isles have cheap wingers in the system so, retaining Nelson on a reasonable deal as the 3C, isn't necessarily a problem if he has turned the corner. I am not advocating to OVERPAY based on need, but you have to balance need with resources and availability too.
But if you trade Nelson, what is your (reasonable) plan to add a 2C and 3C before the start of next season? I am all for improving at the position if possible.
Outside of Duchene as a UFA, it looks like the bulk of the UFAs are a bunch of older players in Spezza, Pavelski, Staal, etc. or even more mediocre players like Brassard.
It is going to be very hard to add two quality centers, let alone not overpay due to demand. Happy to hear suggestions though.