A lot of people saying he would cost 4 firsts... I'd do that for him. Pretty easily.
Habs are a playoff team already, McTavish makes the team better.
So it would be 16+17 this year and 2 picks around the 20-22ish range? That's a lot to trade, pretty easy to do though.
Or, using what people like Lebrun reported the deal with Zegras would have been, 16 + 17 + next year in the 20s + Mailloux? I'd give that up without a second thought.
I don't see McTavish as a point per game player but I think he has a bit more in him, I think he's got 60-70 pt seasons in him, possible having a couple seasons a bit higher than that. 4 mid to late firsts likely won't get you a centre with that quality.
If he ever became available (which I doubt they would), I'd do the 4 picks.