Well, assuming it was strictly a rental then I suppose that’s a different case. But if Stone were willing to extend, it was a huge mistake.
I mean, it depends on the big picture. Let's go back to when the trade was supposed to go down. Valimaki is playing strong in the AHL and had a strong NHL showing to start the year while Andersson had overtaken Stone for the 3rd pairing job and was trusted at the end of games to play with Giordano when we were pulling the goalie, and the Flames had just acquired Fantenburg to play with Andersson while also having Prout. Going into the offseason Flames had 12 million in cap space and tradying Andersson and Valimaki (plus a first) opens up about 1 mil in cap space so 13 million available. 9.5 of that goes to Stone leaving us with 3.5, allowing us to sign one of Bennett or Rittich. Let's assume we sign Rittich to the same deal of 2.75 so we have .75 million in the bank. We can take away most of that .75 for Mangiapane signing for .715. This leaves us with a lineup of
Gaudreau - Monahan - Lindholm
Frolik - Backlund - Stone
Mangiapane - Ryan - Neal
Quine - Jankowski - Czarnik
Giordano - Brodie
Hanifin - Hamonic
Kylington - Stone
Rittich
Gillies/Zagidulin
So we end up with a very unproven back up, and are in line to lose Fantenburg, Prout, and Hathaway to the offseason. Just off of looking at it I trust that d-core alot less in the playoffs. Assuming we sign players Tkachuk and Bennett to the same deals, we need about 10 million dollars in cap space. We could buy out Stone in this prospective world but without someone to replace him on the blue line we're SOL there since we can't re-sign him (with Valimaki gone the injury doesn't happen, meaning there's more of an argument for cap circumventation). The easy way to look at dealing with this crunch is to make some trades. Say, trade Czarnik and for Jankowski, getting whatever we can for them, and call up Dube and sign Rieder for 700k. Going off memory we end up without about 1.5 more in cap space. Now we're getting somewhere. Let's also say we trade out Stone along with a pick and bring back someone like Prout, or get a not so great, but league minimum player in return. That's another 3 million, bringing us to 4.5. Now we can sign Bennett. Nice. Now a combination of trading Neal for no salary, or trading Ryan and Frolik for next to nothing allows us to sign Tkachuk. Let's say we miraculously trade Neal for nothing and end up only losing a 1st. For shits and gigs we can even just say this is where we lost Jankowski. Now let's take another look at the lineup.
Gaudreau - Monahan - Lindholm
Tkachuk - Backlund - Stone
Bennett - Ryan- Frolik
Mangiapane - Dube - Rieder
Giordano - Brodie
Hanifin - Hamonic
Kylington - Prout/Petrovic
Rittich
Gillies
In an absolute best case scenario, we make out pretty good. However we are also right up against the cap and can't have any injuries, especially in net, or our season is done for. Things like trading Stone and Neal for next to nothing aren't realistic so we're looking at it being even harder to get enough cap to sign Stone and would probably need to trade one of Hamonic or Brodie.
All in all, I had no idea what I was thinking writing this all up, especially since I bet no one's gonna read it and I still don't know if I 100% wouldn't make the trade, but I think I've cleared it up in my head a bit more that we sacrifice too much for a stronger top 6 , and would end up turning our strong d-core into a mediocre/below average one for the sake of improving our top 6. NGL though Tkachuk - Backlund - Stone is a dream line and I would have loved to see them make it work, but I'm not sure if it's feasible.