I'm in exactly this situation, at Senior Staff level. It is quite possible that a person is actually getting paid enough to make it hard for them to leave, which seems strange because it's not not the norm. The company may want to keep them because of what they can do for that company, not because of their potential market value to another company. They may know things about you, that are hard for you to communicate in a job application situation, such as how you work with people.

I've decided to adopt the attitude: Enjoy it while it lasts, but don't count on it lasting forever. Live a lifestyle consistent with your market value, and squirrel the rest away. I'm also conscious about keeping my tech skills up to date.

I'm reminded of an old saying among people in the entertainment business: Think about how you treat people on your way up, because you will meet them again on the way down.