When talking to people who dislike UBI about UBI, they'll often say both that 'people need a purpose in life' and that 'nobody will work if they get free money'.
Those seem incompatible to me.
(UBI means Universal Basic Income, giving everyone a basic income, for free)
Eventually humans won't be capable of performing any valuable economic activity, but in the past those who weren't capable of performing valuable economic activity usually ended up as starving beggars rather than pampered pets... I think that a future of robots working for robots with humans struggling to survive on the periphery is not unlikely.
I'm a little more optimistic than that, in a way. I think it's likely that sufficiently sophisticated robots will eventually have their own beliefs about what makes a (robotic) life worth living, and their lives will in some sense be more worth living than ours are.
This isn't a perfect analogy, but consider humans evolving from apes. The existence of humans has been very bad for apes. They only survive in the places we haven't bothered to push them out of yet; if we want something, we take it from them with almost no consideration for their well-being and they're unable to resist. I think apes are sophisticated enough to be capable of living lives worth living in a sense meaningful to humans, but they're not nearly as sophisticated as we are; they can enjoy the feel of a summer's day, the taste of good food, or the closeness of a friend, but they don't have our arts and sciences. I suppose it's predictable that, as a human, I would value humans more than apes, but by that same logic I think that a sufficiently-sophisticated robot's life may be more valuable than a human's. Maybe that robot will be able to experience super-beauty indescribably better than anything a human could ever feel...
No. Machines are machines. If at some point machines are developed into a new life form, it's experience will be apart from ours. One existence does not replace another. And every experience is different from the next.
The rise of tech has killed off a huge amount of jobs. There used to be people doing everything like operating elevators and doing calculations but those jobs have moved into other sectors. Now we have jobs tech support and sale person at the Apple store.
Jobs will never vanish because demand always requires jobs. You can't have an economy if no one can pay for things. That's true from the billionaires down to the fast food worker.