There will be a workforce, it just won't be human-based. Capitalism has always existed without 100% employment, in every example someone needs to work to support others who cannot. Humans have done this under capitalism to support their families and communities, but now we will need to find incentives for robots to do this. It might be as simple as just telling them.

Right but then the robots would produce wealth, but they cannot own it. So you need to redistribute the wealth. Which is, decidedly, not capitalism.

A little bit of wealth distribution exists within American capitalism, through monkey-patches like I mentioned. But full wealth distribution is a new economic system altogether.