Why would he care though?
Let's say I quit my job tomorrow to go to another company, should I feel bad about the problems it will cause where I am? I certainly will not cripple the company as I am mid-management guy, but it'll cause problems. Should I pass on a great opportunity because my poor ex-company and its employees will suffer a set back for a while? No and it should be the same for a millionaire athlete. It is not because they would be rich wherever that they shouldn't be able to choose where they want to work when they have the chance to.
John Tavares reached free agency and he chose to go home play for a great team while being generously paid for it. Every Islander fan would make the same decision in their work life if they could; they would choose the better situation. Asking Tavares to care about the fate of an organization that he served well for close to 10 years is asanine. They failed to build a winning team around him and, as a result, they lost their best asset. If my CEO does a crappy job, people will leave his company and that's on him. Same standards apply.