Ooooh man, all these hard-working comic people here!!
I've been drawing my comic Crow Summer since July, so about two months. But I wrote the first script in 2012 and I've been working on storytelling and concept art ever since then! so I typically say it's four years old. 
I've never abandoned a comic before, although I've taken very extended breaks on my practice comic (which is just about three years old, a little over a hundred pages long, and way more crazy than I intended). It's currently on hiatus now, too, but I haven't forsaken it!
I do have an ending planned for Crow Summer, as I've written the whole script out (several times over). I expect it to take about eight years, Lord willing and the creek don't rise. That's also assuming I only update once a week for that long, and some day I hope to update biweekly. Who knows if that will happen, though.
I also have an ending planned for my practice comic, but all bets are off on how long it'll take me to get there. Haha.