Would the pilot have been killed??

Yes and tortured as well.

Not necessarily.....there were many POWs taken from the Dunkirk area.

But yes, life would be unpleasant for the next few years for that character

Pilots and officers were too valuable for summary execution.
Interrogation, eavesdropping, and prisoner trades were more s.o.p.
In the 1958 movie theres a scene that contradicts my statement.

Could be. I don't know the real story.

I can't figure out why he didn't ditch when he was above the beach which was being occupied by British troops?

More than likely not. He would have been protected by the Geneva Convention and by the fact that Germans viewed the British as fellow Aryans. He would have spent the war in a POW camp. See movies like Stalag 17 or The Great Escape. Russians did not fair as well.

Pilots and officers garner a lot more respect from fellow soldiers.
If he was a sniper, he would have his balls cut-off.