The Flames can do 3 things to get a 1st round pick back:
1) See if there are any takers on Fox --> He is unsigned, and has decided to go back to Harvard for his last year. But honestly, who wouldn't finish their last year in Harvard? Furthermore, I think Adam Fox is more than willing to sign with an American team. Since he is unsigned, I think a pick in the 25-35 range would suffice if a team wants to take that risk on a defenseman who looks like he is going to be an absolute pro. It's unfortunate that he most likely won't sign with Calgary (there is still hope), but we did select him 3rd round in the 2016 draft so it's not entirely bad. The team that gets this guy, assuming we trade him, is not going to regret it. I know he'll be in your top 4 soon.
2) Trade Ferland --> Love the guy, but if there is anyone that probably has peaked value, it's this guy. Can play LW/RW on any line. He was an absolute beast in the 2015 playoffs against Vancouver in a bottom 6 role, and also has played rather well on the top line in Calgary as the RW stopgap for the time being. Has a pretty nasty shot, big body, can hit, he can do it all. Obviously is not a driver, he's a passenger that can really compliment anyone that he plays with. I think the only problem with him is inconsistency. This guy could fetch a 1st rounder (and nothing else) in the 20-30 range, basically for a team that would rather take a flier on a player of Ferland's caliber for a year to see if he can really pan out well to earn himself a better contract. Currently has 1 year left with a value of 1.750m. Pretty easy to fit that within any cap-structured team.
3) Trade Brodie --> If we are looking to really retool and think we have a chance at signing another decent LHD, I wouldn't be opposed to trading Brodie. I really think that this guy just simply did not have a good year. He's usually above average, but this year he has not played well at all. If he were to switch teams and played as their #2/#3, I think he would excel, especially on the right side where he played his best hockey. This guy could fetch a mid round 1st and a B+/A- prospect in my opinion. 2 years left at 4.65m is a dang good contract for someone of Brodie's caliber. Plays above average defensively, and you can expect him to rack up .5PPG.
If I were the GM of the Flames, I would be looking for a 1st in this order. Chicago could definitely give us Nashville's 1st for Fox, or the Flyers could even shell out one of their 1st round picks for a LW like Ferland. The Islanders could very well hand us back our 1st round pick and Ho-Sang for Brodie, because I believe that they are a team that is just a defenseman and goalie away from being really good.
These are just my ideas. I don't think the Flames have to trade Bennett for a low 1st, high 2nd with the risk of him finding his game on another team, or even trade Tkachuk/Gaudreau/Monahan/Hamilton for some quantity + picks. I think with one of these three options we can find ourselves back in the 1st round.