Need a comma before an adverb as last word in sentence?
If the adverb applies to the verb specifically, as in
I loved her passionately
then no comma is required. If the adverb applies to the adjective from which it is separated (in your examples, many and long), a comma would be preferable. Your first example means
How many employees work here, roughly?
and without the comma, the sense is that the employees work in a rough manner.