No – there is nothing on the books that requires you to use the money in your HSA at all. Any money left in your HSA at the end of the year continues to roll over and continue earning interest. If you choose to pay out of pocket for medical expenses without making a withdrawal from your HSA, that is perfectly fine. Your money will continue to grow tax-free.
You can reimburse yourself at any time for qualified expenses. Some prefer to do this once a year while others prefer to do this after each incurred expense. You can choose not to use your HSA at all, which makes for a nice retirement fund in the future.