(can not log in. dislike this computer intensely)
Uh-huh. **Nods vigorously**
I've done some long-distance bike touring and sometimes I, um, didn't plan as well as I should have - which is to say I ran out of food (though, fortunately, I only ran out of water once). But I got through it, and wound up losing weight in the bargain. Humans can survive in some very deprived situations, and I've been through a few very minor examples, and I have to say I was surprised at how much privation can be borne without serious long-term effects. I also learned that fish by itself, no matter how well-grilled, just doesn't do after a couple of days - something was missing (don't know what, I'm not a nutritionist) but when I got back to a place where I could buy food, I ate about two whole pizzas in an hour.
I also drowned a smartphone in a desolate area, which meant I couldn't call for a couple of days (until I got it replaced in the next city of any size I got to), and hence wouldn't have been particularly trackable if someone had been of a mind to track me (as if....I was a boring keg-shaped fifty-ish guy on a beat-up bicycle). The roads where I was travelling (western US, desert/mountain) weren't heavily trafficked, and I wild-camped (which is to say, slept off the roads hidden behind trees or rocks). I suppose a concerted attempt to find me would have been possible, but not without using way more resources than would have been reasonable in terms of people and vehicles. It's amazing how invisible you are when you're a hairy, vaguely stinky guy travelling on a bike with heavily patched bags - people assume you're homeless, if they even notice you. And when you're in the real boonies, unless you do stupid stuff to make lots of noise, no one will bother - you're a needle in a haystack.
In urban areas, the 'being-taken-for-homeless' thing is just weird - you're invisible (e.g., you just don't exist for some people), so I don't think anyone would have remarked on me any more than the 'real' homeless. It means that I can sleep under a bridge on a rainy night; because it's so common for the homeless, it doesn't occasion particular notice. Of course, one well-meaning guy who saw my unshaven self on a street walked up with a fifty-dollar bill, handed it to me, and said "Go do something to help yourself - don't waste it....." so I stayed in a cheap hotel and took a bath on his dime ;-)
I think that the whole disappearing thing is blown out of proportion. There are a lot of middle-class coders here, and lots of people in that way of life can't really see disappearing because they've got a routine. Just go for a hike or ride from a more urban area towards a less urban area, and don't shave or take anything more than perfunctory baths for a week or two, and you slide into a category of human that middle-class Americans just gloss over. Even with a security apparatus hunting for you, chances are good that if you're perceived as local homeless and don't call attention to yourself, no one will ever notice you unless there's way more scrutiny than the PTB want to engage in - I think the implied goal of the bad guys in the hypothetical example is to disappear the protagonist without a whole lot of publicity.