He probably would have been knocked out by a body shot, but have the referee call it a low blow and win the title by DQ. I never saw a guy with more luck in his life than Ruiz in title fights.
Longer than you'd think. Ruiz was a decent boxer with a jab and grab tactics. Eventually, Louis would nail him.
Louis wins every round and stops him sometime between rounds 7-9. John would eat up too many shots for his own good.
This, Louis regularly faced the best available opposition exclusively from the top 10 and regularly from the top 5. He definitely would have defended vs Ruiz.