Ken said he's not planning to quit his job as a software engineer, but maybe to work a little less.
I think he lost fair and square. He looked just slightly shocked when Nancy, his opponent, got the Final Jeopardy question right, since he then knew he had lost (even if she bet nothing, because he'd have less than she started with after his bet). It occurred to me that Jeopardy! is the only game show I can think of where the contestant knows who won before the emcee or audience does.
Ken followed a logical strategy (as always) on his last bet. He bet $5,601, which if he gotten the question right would have given him $20,001, which is one dollar more than the amount Nancy would have had if she bet her whole earnings ($10,000) and gotten the question right (giving her $20,000).
He bet $3,000, $5,400, and $4,800 on his Daily Double questions (he ran into all three of them). He won the first and lost the second and third. If his first bet had been higher and/or his 2nd and 3rd bets lower, for a total of more than $5,600, he would have won the game even without getting any more questions right. Since his total at the time of the first Daily Double was only $4,600 (less than $5,600) and his 2nd and 3rd Daily Double bets were each under $5,600, he would have lost even if he bet 100% on the first Double Jeopardy, unless he also lowered either or both of his other two Daily Double bets.
It's the end of a mini-era and it was fun for me to be paying attention to the news and watching the show now and then as it happened. Now we can go on to the next cultural event of trivial importance!