Update: by the time I got home around 7pm, mosh had started to work
again on PTCL. I tested against my mail and web servers, and then
logged into the office's local network and tested some of their
remote servers over Multinet. It works over Jazz on my phone, too
(I use
https://juicessh.com/).
I also see posts by people saying they can now play some online games
that they couldn't yesterday.
I don't have an emailed update from PTCL (I received one asking for
details this morning), so I don't know if it's a temporary reprieve.