People have been worried that automation will replace workers for a hundred years and it hasn't happened yet, so there is no guarantee it will. I don't know what the best solution is, but if it doesn't include UBI, it could involve jobs programs (like the US C.C.C. during the great depression) or shorter work weeks. Instead of half the people not working and half the people working, you could have everyone working part time, that seems like a win for everybody.