Kill us all off? No, that's too simple, I think. A scary thought I had the other day while considering all of this: If robots are able to do the vast majority of necessary work, the non-rich will fall into three main, employable categories:
1) Great artists/entertainers - musicians, painters, actors, prostitutes, and extending to occupations like chefs, who may even be completely attached to a single elite family to fulfill their desires
2) Highly intelligent - the engineers/scientists who maintain robots and do what little work there is that humans can't do, as well as research and medicine
3) Lab rats
The elite will, of course, want to extend their active lives for as long as possible. They'll have part of that second group working on various cures/vaccines/life extenders, which obviously need trials before the elite will use them. Sure, you could import a ton of monkeys... or you could use some of the 180 million unemployed people in the country at that time. We're already at the point where the oligarchy can write a lot of their own laws, so if such a dystopia were to pass it would be easy for them to do away with any laws against testing on humans.
If one of these participants is really lucky, they'll get the benefit of whatever is being tested with little-to-no downsides, plus pay. If they're only somewhat lucky, they'll die quickly in the trials and their family (if they have one) will get a moderate cash pay out (which is how the rich will ensure the desperate will volunteer). Otherwise they'll come out deformed, mentally and/or physically, but still be paid.