Plan Termination Inquiry;

https://www.ecfr.gov/current/title-26/chapter-I/subchapter-A/part-1/subject-group-ECFR2b7577e2af5412b/section-1.436-1

URL: https://www.ecfr.gov/current/title-26/part-1/section-1.436-1#p-1.436-1(a)(3)(ii)(B) 

Citation: 26 CFR 1.436-1(a)(3)(ii)(B)

Application of section 436 after termination of a plan —

(A) In general.  Except as otherwise provided in paragraph (a)(3)(ii)(B) of this section, any section 436 limitations in effect immediately before the termination of a plan do not cease to apply thereafter.

(B) Exception for payments pursuant to plan termination.  The limitations under section 436(d) and paragraph (d) of this section do not apply to prohibited payments (within the meaning of paragraph (j)(6) of this section) that are made to carry out the termination of a plan in accordance with applicable law. For example, a plan sponsor's purchase of an irrevocable commitment from an insurer to pay benefit liabilities in connection with the standard termination of a plan in accordance with section 4041(b)(3) of the Employee Retirement Income Security Act of 1974, as amended (ERISA), and in accordance with 29 CFR 4041.28, does not violate section 436(d) or this section.
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Please indicate if unpredictable contingent event benefits form part of the exceptions for plan terminations.

I think it's pretty clear from the reg section you quoted that UCE benefits are not included in the exception. The sole exception is for prohibited payments under 436(d) and  1.436-1(d)  that are made to carry out the termination of the plan in accordance with applicable law. That is separate from UCE benefits under 436(b) and 1.436-1(b).

Now, let me ask you - do you have an actual plan that is terminating, provides UCE benefits, has an AFTAP less than 60%, and has had an unpredictable contingent event occur after the plan's termination date? Or is this simply a question of academic curiosity? If it's a practical situation, and if the sponsor feels strongly about having the plan continue to provide UCE benefits after termination, then you might want to put it in the termination amendment and see what the IRS says when you submit the 5310.