[link]http://skeptoid.com/episodes/4115[/link]
You might find this interesting. There's a small possibility that there were "lost cosmonauts", courtesy of Soviet Union who were notorious for covering up information and even destroying evidence.
Frankly, it'd suck to be stuck in space. And you wouldn't last long, our ships aren't exactly designed for long-term space flight. Wouldn't take long for oxygen and food supplies to run out, not to mention fuel, and then you're fucked.
So with any realistic technology, you're fucked. But then again, with our technology it'd be pretty hard to get far enough from Earth to be exactly "lost", but if you'd have some technical difficulty and be unable to return, it would suck just as bad.
And if we're talking sci-fi here, well, imagination is the only restraint. If you're capable of traveling between star systems without dying of old age, either through some kind of stasis/freezing or generic FTL travel, as long as your ship's working you aren't doing that bad unless supplies run out (but if we're talking sci-fi, that can be very flexible, too). If your main transportation method is fucked, then the stasis type of fictional spaceship is probably your best bet - freeze yourself, place some makeshift beacon, and see if you'll ever be found. Which can be 10000000000 years in the future or never. But still arguably better then death of starvation, asphyxiation, or cold. Or not, I dunno.
Of course, I have to say, the above paragraph is purely fictional.
