If, for any cause, any person contributing to the fund shall cease to be in the service of the Department of Fire and Rescue before he shall become eligible to receive any pension benefits, the total amount of the contributions paid into the fund by him shall be refunded in full without interest; provided, however, if any such person shall have had returned to him the amount contributed as aforesaid, and shall afterward re-enter the service of the Department of Fire and Rescue, he shall not be entitled to the pension benefits designated unless he shall return to the fund the entire amount withdrawn, in which event, the required period of service under this part shall be computed from the time he first entered the service of the Department of Fire and Rescue, excluding any period of time during which the member was not employed by the Department of Fire and Rescue. Absent repayment of contributions by the re-entering member, the date of his service shall commence upon re-entry to the Department of Fire and Rescue.