In the past, yes, there have always been other new types of jobs to replace the old ones. But look where we're heading with automation, robotics and machine intelligence. At some point it'll be possible to make stuff for zero financial cost. How so? If everything is automated from the extraction of mineral resources, through processing, to creation of end goods, you don't need money. There's nobody to pay. You just need to own the raw resources, e.g. the land. The owning class can then focus purely on what's always motivated them; living a life of total ease. Start focusing on luxury products created in their automated factories, plus robotic security. They will finally have removed their dependency on the poor to work for them.
And what then? The bulk of the worlds population then simply become a problem to them, competing for the same finite resources. They could suddenly become all concerned about the climate change and overpopulation. Bring on the one child policies and enforced sterilisation. Time to deal with the poor majority. Rise up and revolt you say? Against the robotic security forces and weaponry that are surely coming too? Good luck with that.
It sounds like a plot from a Sci-Fi novel, but it's one possible future, and unless we're very careful, it's possible something like this could happen. So no, sadly I don't think it's safe to just assume there will always be jobs.