N.Y. Comp. Codes R. & Regs. tit. 21, § 5006.2 – General.

(a) The membership of any person in the retirement system shall cease upon the withdrawal by a contributor of his or her accumulated contributions, or upon retirement on a pension, or at death, or when seven years have elapsed since the member has performed service as a teacher which was credited with the retirement system (at least 20 days in a school year), except that a membership shall not be cancelled under the following conditions:
1. (1) when vesting has occurred;
2. (2) where a member who has not had sufficient service to be eligible for a disability and who prior to the cancellation of his or her membership, proves to the satisfaction of the retirement board that he or she was disabled at the time he or she ceased teaching and continues to be disabled from the same disability which caused cessation of teaching;
3. (3) where a member is eligible for a retirement allowance other than a disability; and
4. (4) while a member is on an approved military leave, pursuant to section 243 of the Military Law.
(b) All memberships are cancelled as of June 30th of the school year during which membership ceases.
(c) When membership ceases, interest is credited to the member's annuity savings fund to the date of cancellation of membership if the member was sent a warning that membership would cease. If the system did not send such warning, interest is credited to the date of notification of cancellation of membership. However, under no circumstances is interest credited after the date of death of a member.
(d) Notwithstanding that during the first year of membership, the member fails to render at least the equivalent of 20 days of teaching service, his or her membership will not be cancelled. However, the base period for determining membership cessation will begin with the date of membership.
(e) Notwithstanding the provisions of subdivision (a) of this section, the membership of any person who last joined the retirement system prior to July 1, 1984 shall not be cancelled if such person has at least five years of credited service as a teacher in any period of 10 consecutive years as hereinafter set forth:
1. (1) To retain membership, a member must have at least one year of service in a six-year period, two years of service in a seven-year period, three years of service in an eight-year period, four years of service in a nine-year period, or five years of service in a 10-year period.
2. (2) A membership will cease on June 30th of the year that the member is out of teaching for five consecutive years, unless the member renders 20 days of teaching service prior to June 30th of the following year.