If there is retention on Monahan, Id do it. Obviously a pick goes back to CGY for compensation

Leafs decline - puts them over the cap. Gaudreau would be a better fit as the Leafs need top 6 LW over depth C in Monhan who isn't going to take away ice from AM or JT

Doesn't make sense for Leafs.

Would obviously be great to have someone like Monahan as a 3C, but the 2nd year just makes next season harder.

Would be no way to keep Campbell, hard to pay RFAs at decent rate, no chance keeping Mikheyev (who would be more important with Kerfoot gone).

Then he'd likely be playing with Spezza, Simmonds, types, who are decent players but not really the best to get most out of Monahan.

On the flipside. Kerfoot is a decent player, but he's more effective playing third fiddle with some decent talent (he's good with Nylander, Tavares right now). I think he'd struggle to produce much centring that 3rd line you've proposed.