Mike, as David says, there are two ways things can go. If you, and everyone else with capital want to hang on to the value of it bad enough, then there can only be war, and the reduction of people that you expect has to happen, will happen, but much more than that, the physical end of Earth, we will have destroyed it.

On the other hand, you, and all the others living from capital could authorise the money issuers to begin issuing the funds needed to reflect the value of Joules received from solar. The value of your capital would be instantly lost. But in return you, and all folk would have a very generous UBI, backed by the solar Joules coming from the sun, forever, and by that we would just be doing as a species what a plant does when it first forms leaves, it stops sucking the energy it needed to grow until the point it forms leaves from the Earth, and starts to accept the energy landing on its leaves from the sun as not only the energy it iteslf needs to grow to an adult, but passing on all the energy it doesn't use itself to all the other things on Earth.

If you wish proof with some numbers, it is here: https://eric-bott.medium.com/filling-the-current-uk-economy-50-billion-black-hole-with-light-34f9de4df245