Do you think Zaroff would have kept his word to Rainsford?
The day after meeting Zaroff, Rainsford demands to be let off the island. Zaroff responds by making a "deal" with Rainsford. Rainsford may leave the island on Zaroff's boat if Rainsford survives being hunted for three days.
"I'll cheerfully acknowledge myself defeat if I do not find you by midnight of the third day," said General Zaroff. "My sloop will place you on the mainland near a town."
I do think that Zaroff would have kept his word to Rainsford. The previous day, Zaroff took pains to show that he was a civilized gentleman.
"I have electricity. We try to be civilized here."
In addition to the electricity, Zaroff had a wonderful meal cooked and served it with expensive wine. To not honor his deal, would go against his desperate need to act as a civilized gentleman.
"Oh, you can trust me," said the Cossack. "I will give you my word as a gentleman and a sportsman."
I don't even think that Zaroff would be mad at Rainsford for winning the three day battle. Zaroff might be mad at himself, but he would further respect Rainsford's abilities, knowledge, and ingenuity. If Rainsford would survive, Zaroff would see him as an equal. Zaroff wouldn't see Rainsford as a weak human that deserves to be hunted and killed. He would see Rainsford as strong; therefore, Rainsford would be someone that deserves to continue living.
"Life is for the strong, to be lived by the strong, and, if needs be, taken by the strong."