(a) Except as provided by Subsection (b), if a disability retirement annuity is discontinued, the member is entitled to a lump-sum payment from the retirement annuity reserve account in an amount, if any, by which the amount in the member's individual account in the employees saving account at the time of disability retirement exceeds the amount of payments payable before the date the annuity was discontinued.
(b) The benefit provided by this section is not payable to a member who, after discontinuance of a disability retirement annuity, returns to state service or elects a service retirement annuity.