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 Sec. 4041.28(c) or Sec. 4041.50 of this chapter (whichever is applicable); or
(b) Paying the PBGC a designated benefit in accordance with Secs. 4050.4 through 4050.6 (subject to the special rules in Sec. 4050.12).