Generally a plan will allow you to leave your assets in there indefinitely, but this is probably not ideal for you. Most custodians will be happy to hold onto your account dollars as long as you’re willing to leave them there.
They don’t have to spend any time servicing your account since you can’t make contributions and probably aren’t even able to reallocate your assets, and they will continue to make money on your account with the built-in fees. You may be charged inactive account fees or small account fees as well.
It would be quite rare for an employer or custodian to force you to take your assets out of the plan, but every plan is different, and there may be such a rule.
Rolling over your assets into a Traditional IRA would probably be better, to have more control over your assets, more investment options, and lower fees, in all probability.