I'm not sure I follow
Wouldn't UBI be funded by the wealth generated by the automation in this case? So is the difference only the amount people receive that changes UBI from an economic cushion to sharing the wealth?
In addition the premise that everyone will be fired is a little presumptuous to me. So far we've seen that agents are very capable of automating well-scoped, verifiable tasks but the majority of jobs don't consist of those
You assume that the people who are at the top of the organizations generating said wealth will have any incentive to do that. Look around the world at the petro states for examples of a highly capital intensive industry generating money that subsidizes the rest of the economy.