I don't think you see Dubas do the 1st Rd pick for a rental. It's something going back to the Muzzin trade he has always mentioned not liking to do. He said repeatedly that last year it made sense for them to do over any year because of expansion coming, coupled with the shut down of leagues for prospects and limited scouting.

Funny enough that the year Dubas sells himself on actually trading a 1st for a rental, he gets burned with what is the ultimate risk with rentals.

I doubt Buffalo would retain.

Certainly Ollasson's production is better than Kerfoot's by that doesn't make him a better player. Leafs at some time when the flexibility of Kerfoot to play centre or LW. Besides it's an overpay for him as proposed.
Any trade involving Dermot exposes to Leafs to going with unproven NHL Dman.

I would hate to see Olofsson traded, but getting Kerfoot and a first has me interested.
Retain 50% of Olofsson, take Dermott out of the trade as Buffalo has many options for LHD and add another piece.
Buffalo traded away 26 yo Ristolainen and 25 yo Reinhart while shopping 24 yo Jack Eichel.
I think if Buffalo is looking to the future trading 26 yo Olofsson makes a ton of sense as Buffalo has other options for LW especially if Kerfoot is part of the trade.