If you immediately terminate the number after 12 months + 30 days then you have quite aggressive timers.
Credit expiry is as expected, though we had a transitional stage which lasted another year - inactivated. At any point during the second year the number could be reactivated by the user by applying credit and contacting a csr, though once that second year was up the service was terminated and the number released into the available pool.
It sits in a terminated state in the system for some time longer than that, for around a month. But if you haven't topped up in that long then yes, you will be deleted. Licenses cost money! My previous telco deleted you the day after you were terminated (on the same 365/395 day schedule).