That is assuming you can bring in someone for the $8 million in savings that can match his contributions on the ice. If not you are throwing money away.
We also don't know the parameters around not wanting to retain. It's possible Noone made it worth their while to be convinced to retain.
That is the calculation every team has to do to decide whether or not to retain in a trade. But in every case they are dealing with a sunk cost. They get to choose between paying the full contract or some lesser amount, not < 50%. They can save the rest of that contract.
To decide that a player needs to be moved for the good of the team's culture, you are going beyond direct, on-ice contributions. To do that and then refuse to retain doesn't make sense.
In this case, you need to consider Wheeler's age. He is highly unlikely to contribute as much as he did last year. He didn't contribute 8 mil worth last year.
Can you replace his contribution for 4 mil? Depends. You may not be able to find a player available to make that contribution regardless of cost. But you had previously decided that he needed to be moved. So you move him for the best offer and replace him on the roster with the best player you can find. The value of the trade return is completely unknown here.
We know they said they were not interested in retaining.
With heavy retention, he should have also brought a return with some value. That may or may not have been possible early in the off-season. It was not later, after teams had made their moves. This was a strange year for off-season moves so the equation may not have followed normal values.
But from an owners POV, you are still left with move him and spend 8 mil, or keep him and spend 16. You need to fill his roster spot so you need to spend 9.5 mil, not just 8. Save 6.5 mil .... in your pocket.