oh yeah, you gotta know where it ends. you also need to know at least vaguely whats gonna happen in the middle, otherwise thats gonna be... a mess.
comics theoretically could go on and on, especially slice of life comics with decent characters. but hey, look at marvel and dc - they run on and on and on by creating new arcs, constantly. to an extent, it works, but honestly they both have awful continuity and every so often they have to have an apocalypse to keep iron man 20. either way, these comics have arcs that have a planned ending, so i dont think its really possible to write a story with a plot without some kind of ending, even if its lots of small ones.