Did you pay attention?
The world coming at Wakanda was Namor's entire game plan.. He's counting on it. Something you say was never on the table is instrumental to his master plan.. He's waiting and counting on the world coming at them.
Wakanda was being blamed for sinking the ship.
It was already in motion.
There one outside government contact was immediately compromised cuz the took the bait beads.
Namor KNOWS eventually the world will come for Wakanda, and he pointed out at things are, they have no allies and will come to him
That would have been the case regardless. The world was going to come for Wakanda
So you can't say that there's no chance when that's exactly what was going on and why Namor agreed to retreat.
Only difference is had he not revealed himself.
1. Wakanda would have no black panther protection
2. Wakanda would have been even more vulnerable for attack if they were completely focused on Val and the CIA due to not even knowing there was another powerful enemy