I'm operating under the assumption that Tarasenko is not returning before rosters expand, which should be a given.
Even with a trade AND one of Kostin/Kyrou sticking on the roster, you only have to waive DLR and Brouwer to get to a 23 man roster when everyone besides Tarasenko is healthy. We should not reconsider an improvement to the top 9 over concerns about waiving either of those guys. Those two are the definition of expendable forwards and losing either to waivers shouldn't be any cause for concern.
Realistically, Kostin is pretty clearly not going to stick. Right or wrong, Berube doesn't trust him beyond a 4th line role and barely trusts him in that role in a close game. I think Yappi is dead on in his assessment and frankly I think Berube's stance on Kostin at the moment is fair. I've liked what I have seen from him so far, but I also haven't seen anything to indicate he absolutely needs to be playing in the middle 6. I think he played well in a bottom 6 role last night and is absolutely better suited for that role than Kyrou would be. I'd leave him up here for a few more games in the same role. Get him a few weeks of practices, a couple big NHL paychecks and send him back to the AHL with a list of things to work on.
And then you call up Kyrou and plug him into the middle 6.
But none of that causes me to stop looking for a trade. For the sake of argument (and knowing Berube's affinity for Sanford) lets say we are married to that Sanford-Thomas pair on the 3rd line moving forward.
Schwartz-Schenn-Bozak
?????-ROR-Perron
Sanford-Thomas-?????
?????-?????-?????
Kyrou, Barby, Sunny, Steen, Mac, DLR, Brouwer are the options to fill in those ????? lineup spots. I want Kyrou on the 2nd or 3rd line and I want Barby-Sunny-Steen as the 4th line. That leaves a hole in the middle 6 that I don't want filled by Mac, DLR or Brouwer. So go out and get an acquisition to fill the hole, waive whichever of DLR/Brouwer you like the least.
Schwartz-Schenn-Bozak
New Guy/Kyrou-ROR-Perron
Sanford-Thomas-Kyrou/New Guy
Barby-Sunny-Steen (AKA the best 4th line in hockey)
Assuming that new guy is a 40+ point player and Kyrou is a competent middle 6 skill player, that is the deepest forward group in hockey while also having a pretty damn legit top 6. It leads to a tough decision when Blais returns if everyone stays healthy (lol), but that is a great problem to have.