A post from Arthur Hlavaty alerted me that a collection of the late Donald E. Westlake's nonfiction has been published, under the title The Getaway Car. I meandered down to my local independent bookstore to see if they had it. They didn't, but they could easily get it from their distributor, and, while I was at it, I asked for the two posthumous Westlake novels I'd never gotten around to buying or reading, which we found in the system even though I hadn't been prepared to ask and didn't recall the titles offhand (ironically, as one of them is called Memory). They all went in with the next day's orders and arrived the day after that.
I've now read all three, and for good measure re-read a couple other books I'd forgotten everything about when I compiled my annotated Westlake bibliography, and updated it.
Neither of these posthumous novels is humorous, and I suspect that if Westlake had published them, he would have used one of the pseudonyms that he kept around for most, though not all, of his grimmer material. Much of that material is not to my taste, insofar as I've tried it, so I just left the pseudonyms out of the bibliography, but as I've included everything else originally published under his own name, I covered these.
I actually liked them both; they're tough and searingly memorable, even the one about the man who's losing his memory. Westlake withdrew The Comedy Is Finished from potential publication because of the release of the movie The King of Comedy, which is also about the kidnapping of a TV comedian. Why he never published Memory, which had been written much earlier, I don't know, but by the same token he would certainly have withdrawn it if it had been in the pipeline when Memento was released.
In both cases, though, they're very different. The King of Comedy is kidnapped by a wanna-be comedian who wants a spot on his show. In The Comedy Is Finished, the kidnapping is by a small gang of leftover 60s revolutionaries who wish to use him as a bargaining chip to get their comrades out of jail. That he's a celebrity is strongly relevant to the plot; that he's specifically a comedian is somewhat less so, though he does have to be quick-witted.
Memory is actually sadder and bleaker than the movie Memento, because this guy is losing not only his post-accident memories but his pre-accident ones as well, so instead of having a base to stand on (however mistakenly), he's sinking into the mire. Also, where Lenny in Memento loses his new memories within minutes, contributing to a frantic, goofy tone to the movie, for Cole in Memory they slowly fade away over a period of weeks, leaving ghosts of themselves behind, so he sinks more slowly and finds himself more lost. There's a couple points in the story where he tries to act on the basis of what he does remember, or of what he's left himself a note to do even though he no longer remembers why, and those are particularly bleak and, well, memorable.