One of our clients just got that same letter.... Unfortunately, "some" in this industry think this is a legitimate tactic - as filing under DFVC has a price tag associated with it - and "apparently" the 45 letter lets you off "scot-free" if you meet the deadline.
I think it is a very, very dangerous practice....
Assuming the Plan performed the termination correctly, and passed the info and $$ to the PBGC correctly, the Plan is done. Provide the participant with the PBGC contact information.
Hardships under facts and circumstances can be for almost anything. There are many financial considerations to consider, though.
From: https://www.irs.gov/retirement-plans/retirement-plans-faqs-regarding-hardship-distributions
So, if they have a brokerage account, or a pleasure boat, or even a coin collection, then they may have other resources available.