If I am Columbus and their big free agents aren't staying, I would trade both Bobrovsky and Panarin rather than lose them for nothing.
Sustained success is more important than one shot at a playoff run. Getting two first round picks, two prospects, and 2-4 other pieces of varying value could put Columbus in a position where they have the currency to add players in the upcoming off season. An example of this would be that if the Islanders had traded Tavares at the deadline, they would have been likely to get the kind of pieces that could have formed a big chunk of an eventual Ryan O'Reilly trade package. Is O'Reilly as good as Tavares? Maybe not. But the Islanders would be in a much better position right now if they had the currency to replace Tavares in the off season while coming close to breaking even.
Teams don't have to use picks to select prospects, they can be used as currency in future trades, so it makes no sense for a team in Columbus' position to pass on the kind of currency they'd get in return for Bobrovosky and Panarin in order to get one last run out of both of them.
Panarin? Sure - everything you say makes sense. Still - the way i've always looked at it is there are two sides to every coin.
Forget Panarin and Bob exist for a minute. Think strictly of Columbus, in a playoff spot, near division lead, and thinking they have a legit shot at contending this year. TDL is approaching. If they decide they are 1 player away from contending, they'd normally add at the TDL. Wouldn't the opposite be true? Yes they might lose Panarin for nothing - but who would they trade him to? A team in an exact same position as they are who would pay a 1st round pick (let's suppose that's the cost) to land him? Why wouldn't Columbus do the same, and just keep him and go on their own run?
I won't get into Tavares because I disagree strongly, but no point opening that can of worms here.
The one thing that is completely unique is Bob and a #1 goalie. It's one thing to trade away a Panarin - if you do, you still have forwards, you still have wingers, etc. The gap between a #1 goalie (and a vezina caliber goalie) and a backup is often night and day. It's the one position you can't afford to lose. Trading Bob away is the equivalent of throwing in the towel. It is NOT the same as trading Panarin away.
To be fair - i'm not very familiar with who their backup goalie is. I suppose if he's a complete stud and they have faith they could go on a strong playoff run with him, maybe trade Bob too.