(a) The retirement annuity of a disability retiree may not be terminated under this subchapter after the earlier of:
(1) the date a disability retiree attains age 60; or
(2) the date the disability retiree would otherwise be eligible for service retirement under this subtitle.
(b) The disability retirement of a disability retiree described by Subsection (a) is considered for all purposes under this subtitle as a service retirement.