Like any relationship it can work and it can fail.
The important thing with online dating is to actually plan to be with the other person, serious plans - If you haven't already met up with them. If you have no intention of meeting then you might as well just not bother as there needs to be a connection that can only be made when two people are together.
Of course for some people, they are just distance relationships as they have the means to see each other every so often, they can't help living far apart.
But anyway, love is in the heart, distance is in the mind.
If it's meant to be then it's meant to be. If not, then it's just like any other relationship that fails.