The plan administrator of a terminating plan must distribute benefits for each missing participant by—
(a)
Purchasing from an insurer an irrevocable commitment that satisfies the requirements of § 4041.28(c) or § 4041.50 of this chapter (whichever is applicable); or
(b)
Paying the PBGC a designated benefit in accordance with §§ 4050.4 through 4050.6 (subject to the special rules in § 4050.12 ).