So would I! Over the course of the novel Sam becomes a worse person (cheats, endangers others, etc.), and by the end he's pulled back from the brink and gained a level of maturity. At that point he's not as insular as he used to be. He was once happy to while away his life in a town in the middle of nowhere, but now he's open to more of life's adventures. Whatever he's going to achieve in life, he's going to have to work for it. I do wonder what happens to him next. I have it in the back of my head that he and Mrs Cholmondeley team up again about 10 years later in another story. But I doubt I'll ever write it. The world has enough sequels.
Maybe the world does have enough sequels, but good characters are tough to create. I mean, I don't think Harry Potter (it was only a matter of time before he popped up in YA fiction discussion, eh?) was a particularly good character. A character in an interesting setting with an interesting back story, but as an actual character, I think that Timothy Hunter from Neil Gaiman's The Books of Magic is a much better character. He's darker, he's more human and more flawed. Both characters have a certain darkness and temptations of power and fame exist for both, but Timothy Hunter is painted much more vividly. I think seeing Sam progress into . . . wherever could be fruitful, especially if as mk said, ". . . that sinister nature of Radium Baby were turned up a notch or two". There's a lot of room to play with character arcs and characterization in a world with cannibal bishops, mad, gibbering financial geniuses strapped to boards and radio contests that willfully endanger the lives of minors for advertising revenue, no? I dunno, it seems to me that if I created a universe I'd want to find out what's hiding in its fundamental fabric.
I'm curious, did you have other endings in mind and have to choose one or did this book flow out of you in the manner in which we read it? I'm always curious about what paths art could have taken. It's a reason I love to hear early mixes of music or paintings that are half finished etc. The process is cool. I'm really curious if it ever occurred to you that one of them was the Radium Baby? Did you always know while writing it that none of them would be? Also, did you ever play with the idea of someone else actually being the Radium Baby or that all three of them were (my triplet theory)? Also, and be honest here, Gloria and Sam hooked up in Egypt after Hadrian took off in the autogyro, didn't they! I knew it. edit: What I should have written is "did it occur to you while writing it that none of them would have been revealed to be"
Already writing your own slash fiction?! Hell, Sam and Hadrian shared a room, you never know… But I am almost certain Mrs Cholmondeley and Clive Chapman have shacked up or will shack up at some point. Actually this leads into a whole question of writing diversity. I try to get a balance of characters who are female, black, gay, etc. I got a good number of ladies in Radium Baby, but no black characters because it was the 20s and black people weren't really running radio stations back then. Then that leads me to wonder if any of the characters are gay. Sam is straight, but Hadrian and Gloria are up for grabs. Hadrian is portrayed as being a little bit "girly", but that doesn't mean much. For that matter Gloria can be fairly butch at times. I don't think I had any other endings in mind, but then I don't plan ahead in any great detail. A lot of spontaneous flourishes turn into key parts of the story, and I can't think up spontaneous flourishes in advance. Some people can — but as you know everyone has their own creative process. A necessary corollary to being spontaneous is you have to go back in the editing stage and rewrite a bunch of material that was crap. There is a lot of Radium Baby on the cutting room floor. How do you find it when you're writing songs and albums? How well do you know your music in advance? The only thing I know about the real Radium Baby is that it's not Sam. It could be Hadrian or Gloria, but nothing like that is ever hinted at (at least intentionally). Most likely it's someone else entirely. I think I might have imagined it be Gloria or Hadrian very early on, but nothing like that even made it to the first draft. If you want to hold on to the triplet idea, there's nothing stopping you! Nothing in the novel says it's impossible, and I like that ambiguity. You get to imagine your own ending.