Edmonton is in full win-now mode, for better or worse. Losing Puljujarvi makes us worse.
The problem with everyone you've mentioned is they're a gamble. Blackwood sucks, at least lately. Absolutely no way can we go into next season with a Blackwood/Skinner tandem, they'd get chewed up and spit out. Smith is struggling, very young, and LD isn't really a need for us since I think we'll keep Kulak, who's been very good for us. Zacha is hopeless defensively, Puljujarvi is our best defensive forward.
Right wing is our weakest forward position, and Puljujarvi is the best one we have by far. Losing him would be brutal, keeping him needs to be one of our highest priorities this offseason. Keep in mind, we also have Dylan Holloway NHL ready, who can play C and LW, so shoring up C/LW isn't a priority.
As for where the space will come from, Kassian is a cheap buyout if we can't find a taker (less than a million over four years) and Barrie will have value from his point production. Kane is the wildcard, for sure. We might not be able to re-sign him, but if we can't, it's even more important to keep Puljujarvi.