In his last book Heinlein was feeling kind of sorry for all the poor helpless characters had written about over his long career. So he had them hop into a time machine and he saved all thier lives. Well, most of them anyway. It was a rambling and pointless book, but I still liked it. Just as I kept reading Rice’s Vampire books long after it was clear that she had nothing new to say on the subject and was in fact repeating herself.
Heinlein’s last big fiction inventon was World-as-Myth, in which everything any writer cranks out is turned into reality on some alternate time/space/diminsonal lines. So he ends the book and his writing career the only self respecting way he could have—They All Lived Happily Ever After.