Assuming that no other leave laws apply, termination is an option. That said, you may instead want to consider offering the employee an unpaid personal leave of absence or revisiting whether a flexible or part-time work schedule would be better than losing the employee entirely. Recruiting, hiring, and training are all expensive undertakings (generally from 20 to 200 percent of their yearly salary). Terminating an employee without considering other arrangements might also have a negative impact on employee morale and your reputation as an employer. If there’s a way to keep an employee around — even if they need some time off — it would likely better for your bottom line.
If you do decide to terminate an employee who is out of leave, make sure you are consistent in that response going forward. If you are flexible with some employees while terminating others, you will open yourself up to claims of discrimination.