You can do that with any volatile asset (e.g. penny shares or some weird option or whatever). But the whole reason why these assets are volatile is because they might not come back. Any number of things could happen that would cause the price of bitcoin to plunge irreversibly - a bunch of countries could get together and start imposing restrictions on it, or someone could discover a massive security vulnerability, or the community might decide en masse that some altcoin is better and switch to that, or the techno-libertarian weirdos might just get bored of cryptocurrency and develop a new obsession (my money is on 3D printed Magic: The Gathering funkopops).