Why would the guy retire and leave money on the table? Multi-millionaire or 75k union guy that scams the system to go out on disability vs. retire out right. He can stay the course, the team LTIRs him, insurance reimburses the team, and he gets paid his salary. Rarely does a person of sane mind walk from cash.
With respect to LTIR vs retirement, in this case we will use Ladd (but this goes for other potential players as well), I would assume it depends on several factors, with a couple details still to be determined.
The most important would be the amount of remaining money and how much, if any, insurance will cover? If the Isles can recoup a significant portion via insurance, then it makes sense for both parties to simply use LTIR.
However, if insurance is not necessarily applicable, be it the contract was not insured at the onset of the deal, the last few years are not insured for a material amount, his career-ending injury is not covered under the policy, etc. then both parties can look at outright retirement - with a few caveats.
The big question then is are Ladd's remaining bonus payments guaranteed if he opts for retirement and/or if the Isles agree to pay them out if he retires? The $6 million remaining in bonus money is the money I could see Ladd NOT walking away from. If the money is guaranteed or can be negotiated as such, even for a premature retirement, then retirement becomes a reasonable option.
Especially since Ladd only has $3 million in base salary remaining at $1 million per season. But that isn't necessarily a true and full $1 million per over three (3) years. Depending on how the CBA re-negotiations work out, escrow and/or a salary-percentage haircut could bring it down significantly.
At that point, you could argue that Ladd retiring and taking a front office position, with a contracted salary, no escrow, no haircuts, and potentially different tax considerations, could earn him more money then the $1 million AAV. If that is indeed the case, then retirement and not having to deal with medical paperwork, physicals to remain on LTIR, etc. could be the best course and very palatable.
We just don't know enough right now to make a firm call one way or the other. And that could be what the Isles and said player (be it anyone from Ladd to Hickey) are also waiting on. They might want to see how the new CBA breaks down and then decide on what action is best for everyone.