I'm new to flash fiction, but from what I've come to understand, it needs to have all the same components as a regular fiction story, from character development to conclusion. My question is, does the conclusion have to be....well...closure? My story is about a man being hunted down for a valuable object he possesses, and the very last line of the story reveals the importance of this object. Basically this object proves extraterrestrial life exists. Can this suffice as an ending? It's open even though it wraps up the entire story nicely.
It's generally acceptable for shorts and short-shorts to end with a "capstone" of sorts, without necessarily concluding all the dangling plot threads. Consider The Nine Billion Names of God, or to a lesser extent The Veldt, both of which reach a perfect final line and then end there without dragging things out any longer.
I think if anything, flash fiction is better suited to an open ending than longer formats. There's less investment on the part of the reader, so people will often be happier for things to end on a wham line, leaving the consequences to their imagination.