The branch office will appoint another circuit overseer in due time
I would say this has more to do with the one CO and is not indicative of retiring all CO's.
I seriously doubt the pink-slipped CO would've been allowed by the Society to contact congregations with such a letter if his "reassignment" had related specifically to him for some confidential reason. The only communication would be official and come directly from HQ bearing some camouflaged language. Plus I doubt the guy would've feigned such cluelessness in his letter if he was aware something really was up with him and his wife.
That seems to indicate that they're not getting rid of or decreasing the number of COs in general, but are maybe getting rid of the older ones who are getting to the age that they might be more trouble than they're worth.This guy's letter clearly indicates he's been told absolutely nothing, including whether a truly new CO is being assigned. He's likely merely assuming. He knows for certain only that he and his wife were given the boot. So it could be all of these scenarios, some, or only one.
What it's very unlikely to be, however, is 'none of the above,' imo.
AMNESIAN
Captive 7/1972 - 2/2001