Overlooked line: You're a minute late... I give the whole thing back
Browsing the board there is so much confusion and dispute over the movie's ending. But it was plainly telegraphed well in advance.
LONDON:
Shannon, why don't you brief us on your strike plan?
You coming along? There's nothing you need to know about.
The colonel's due at the garrison...at 0500 hours on the 25th.
That's 5 a. m. You're a minute late...
I give the whole thing back to Kimba.
You're working for me, Shannon.
You could fire me.
(setting the stage for)
AFRICA:
YOU'RE LATE!
What the hell's going on? Who's that?
Colonel Bobi, you are under arrest.
President Okoye.
I am president.
You're nobody.
Shannon, get him out of here. This whole country's bought and paid for.
You have to buy it all over again.
In short Shannon stated his terms, his terms were accepted by virtue of his sponsor not firing him, and and followed through to the letter. They were late, Kimba was dead, so Shannon gave it back to the next best candidate.
Moral of the story: Men of good character realize punctuality is important.