The System may allow an individual to repay this refund through: a tax-deferred lump sum payment in full; substantially equal monthly installments over a period of at least one but not more than 24 months by reducing the annuitant's monthly benefit over the established number of months by the amount of the otherwise applicable contribution; or a combination thereof. To the extent permitted under the Internal Revenue Code of 1986, as amended, for federal and State tax purposes, the monthly amount by which the annuitant's benefit is reduced shall not be treated as a contribution by the annuitant, but rather as a reduction of the annuitant's monthly benefit.
If a member makes an election under this subsection (c) and the contributions required in items (1) and (2) of this subsection (c) are not paid in full, an additional one-time lump sum refund representing contributions made following the previous refund shall be provided to the named beneficiary or beneficiaries on file with the System or, if none, to the member's estate, when the member dies.
40 ILCS 5/16-143.2