Indeed, with a big BUT: you don't want to overvalue loyalty in respect of competence. You don't want to have a boss that is not good but "is here since forever".

Instead, reward them economically. Everytime the company takes a leap forward, make clear to them that they were important for the process, and share some profit.

And make clear that being important in a moment doesn't automatically mean they will be important in the future: they will have to compete on results, like everyone else.