Im not sure if I fully understood you but..
All users in Payza from US cannot do anythign with funds in their account in Payza.
All those funds are frozen for ever and cannot be withdraw from Payza
Those who live outside US can still do whatever they want in Payza, since Im from European and I can still send and receive money
Withdrawing money from my Payza account to my bank account should be simply.
Thought I havent tried it yet but who knows how it goes when I do.
And who knows if FBI pam pam Payza and shutdown it foreever.
Buuut like I mentioned can US force UK company to shut their business.
Who knows.