Why, after the botched burglary, did Sykes go to such lengths to keep Oliver alive? The boy was no use to him, and he would have escaped easier if he had been alone.
Y'see, madness, as you know, is like gravity. All it takes is a little...push.share
Sykes wasn't a complete psychopath. He knew that Nancy had a soft spot for Oliver and that he would catch all kinds of grief from her if he didn't bring Oliver back alive. And besides Sykes liked Oliver because unlike most people Oliver had the courage to stand his ground against him.
The players of The Game are the scum of the earth
Well the answer to your question is "the story needs it."
The real question should become "why did the adaption waste so much time putting them in danger when virtually everyone knows they get back anyway," as the situation they get put in has more danger than Sikes would reasonably stick with Nolly in.