At the end of ST:DIS 3x05,
Nhan decides to stay with Barzan scientist Attis on the Tikhov.
Her rationale is that he does not want to leave the ship
where his dead family rests. He is terminally ill himself from the event that killed his family.
As far as I understood, the crew of the Thikov is a rotating assignment, anyway, so all Federation members are in charge of the ship from time to time.
Burnham points out that Nhan staying on the Tikhov means her Starfleet career is over.
Why is that? Wouldn't it mean at best an extended leave until the next regular crew for the ship can be assigned?
Or, if you will, until she has stuck around for Attis' family to get a proper burial?
Especially with the current state of Starfleet and the Federation, it doesn't seem like they can be overly picky if a capable, trained officer were to rejoin even after a prolonged absence.