Quoting: HabsRafiki
Unless there was some mystery ailment that kept him out of the last three rounds of the playoffs, Tatar won't be back even if the Habs wanted to keep him. Given that he's 31, that's probably not terrible news for the Habs.
Danault has upped his value in the playoffs, but I doubt he gets a $42M package. I'd wager it's closer to the $30M (6x$5M) he was offered at the beginning of the season. There will be other suitors, but the market for a checking centre is fairly well established in the $3M to $5M range.
Unless you were getting a third year out of KK, that's too much for a bridge. Given his performance, he'll be much closer to $2M, maybe even a shade under.
I won't comment on the rest as I don't think the Blues need Weber and I know Price would never accept a trade to Ottawa. I suspect both will have some weird surgery on the eve of training camp, allowing the Habs to eclipse the salary cap by oh, hmmmm, $18M or so.
I feel like Tatar would be willing to come back if the Habs promised Ducharme wouldn't be making lineup decisions anymore. Given that the team was substantially worse by nearly every metric after Ducharme took over, that seems like a good idea anyway.
Danault's the top UFA centre in the league this year, which'll drive up his value a good chunk. As I said, I actually have him under the evolving-hockey projection, and the Younggrens have never been accused of overvaluing being the 1C on a Finals team.
I just gave KK the EH projection under the premise that on a deal that small the specifics don't matter much. Your mileage may vary.
As for the Blues getting Weber, I dunno how much immediate help they can get for Tarasenko given his health. Weber might actually be the (perceived) best player available in a Tarasenko deal, and it makes the money work nicely. If nothing else, given that the Oilers reportedly want to pay real assets for Duncan Keith, I feel confident that the Habs could shed Weber's salary and potentially acquire Tarasenko for futures.
As for Price, maybe. The Habs can always functionally end his career if he doesn't waive by refusing to play him, so they've got a whack of leverage to work with there. Even if they can't, moving either Anderson or Drouin and Edmundson or Byron can always free up the cap space anyway, so it's still feasible to do this if Price sticks around.