So in some sense he's safer in the embassy than he would be living in Ecuador proper. Because the US is willing to illegally kidnap people but won't dare to mess up the embassy system.
They don't seem to do much of that kind of kidnapping to put people on public trial, do they? The only case I know of was Eichmann's extraction to Israel. I assumed (but I'm not sure) that those kinds of operations were kept secret.
All that to say, I doubt they'd secretly kidnap Assange to put him on trial in the US for... publishing documents given to him by other leakers? It's not exactly a clear cut case, I don't think. It'd be more politically agreeable to kidnap some terrorist for that kind of thing.
No, we don't do so much kidnapping (unless it leads to trial-less imprisonment at a CIA black site) as assassinations (the most public being Osama Bin Laden, of course).
If he went missing in Ecuador it could be spun as "local gangs" or something. If he were to go missing or end up dead in the embassy there would be a lot of fallout.
