The term “hanging on” can be open to interpretation. For example, you can probably keep your spa manager job as long as your facility keeps paying its bills (and its staff) on time. In another scenario, your spa might be running in the black, but you're feeling like a burned-out hamster unable to get off a rapidly accelerating cage wheel. In that case, you'll probably hang on only as long as you can keep your fast-disappearing sanity.
Finally, you'll likely keep your spa manager job as long as it's personally satisfying and professionally challenging. If you become a little too comfortable, or downright bored with it, you might start hunting for greener pastures.