Entering Namibia with a passport from US that expires in 5 months. In Namibia for 7 days with ticket to leave. What will happen?
As stated in Timatic, the database used by airlines:
Passports and other documents accepted for entry must be valid for a minimum of 6 months beyond the period of intended stay.
If the check-in staff is diligent enough, they'll check this and deny the passenger boarding.
If they make it to Namibia, they'll be kicked straight back home and the airline will be heavily fined, and will make the passenger pay for it and could ban them from flying with them again.
So in short: just don't try!