Calgary isn't retaining on that term.

Columbus obviously declines.

I have reasoning on how the trade can work as the Dubois trade is recent proof that contracts won't be as untradable as previously thought.
That being said, the only way I see Columbus interested is with the retention due to the contract length. Calgary could very well refuse due to the length of the contract and prefer to keep huberdeau with hopes of better surrounding him with more elite scorers to have his offense pop through.
The idea behind this hockey trade could make sense both sides as Columbus will have trouble trading Laine as well. Waddell has already admitted that he probably is looking at a hockey trade where Laine is sold on a minimum and will need to looked at all options to have their best possible return.
But you do bring up a good point. Calgary for this trade to work has to retain! That length of retention could be a major holding block.

Columbus is going to get pennies on the dollar for Laine. He has been injured, rarely produced as a result of past couple years and has a big contract. Plus it is now public knowledge that Laine wants out. Their only hope to get something back is a bad contract with potential to be a better deal for them hence a hockey trade. Something Waddell already alluded to as a big possibility.
Columbus may have to give up picks/prospects to trade Laine as some analysts and experts predict. Here I found a proposal where they gain picks and have a potential bunch back player. Huberdeau probably doesn't reach 115 points again, but with better elite players like Fantili the potential for 65+ points is still there.

Columbus will not take on one of the worst contracts in the NHL to get rid of Laine. Waddell also said that if they don't find anything that doesn't make sense, they will look into holding onto him for the time being.

Yes we know. Still not taking on hubby. Age cap hit and term are 3 large red flags. We can take on short term money. Definitely not taking on long term money, especially old, expensive, long term money

Huberdeau requires a very specific type of center to maximize him. Columbus does not have that center. Columbus is also content to hold onto Laine for an ideal trade, as Waddell said, so this is a no-go. Huberdeau wouldn't be any better in Columbus than Calgary, and the contract is several years longer than Laine's.

CGY won't have cap issues for a while. Using a retention slot for 7 years isn't worth Laine. Huby will end up playing out like Benn did in Dallas.