My convoy's status is stuck at "attacked", what can I do?

As long as Ubisoft does not release a patch: No, you won't get it back. It is a known bug, at least for the community, Ubi does not seem to care too much.

I lost mine when a convoy was attacked and I closed the game instead of trying to save it. Next time I started the game, the convoy was still under attack, but no way to save it.

Edit: Does not seem like Ubi would patch it soon. The Holiday Patch from Dec 18 fixes numerous bugs, but not the Convoy bug – which is listed already on the second page (of currently 101) in their official bugs thread.

Edit 2: Neither did Patch 1.03 fix this bug.

Edit 3: Patch 1.06? lol. As if they cared.

It's a bug for sure. I have a full inventory of convoys and they're fully upgraded. I know how to defend them myself if attacked or how to send my assassin recruits in my stead. I make a lot of money off the convoys, although I've quickly run out of things to buy or use them for, and I use them often.

When one of my convoys got the bug, I received a notification saying it was being attacked. I was busy doing something else at the time, and honestly, I didn't want to go through that tiring routine of saving it myself — though it shouldn't have gotten attacked in the first place, as I'd already removed the risks of an attack.

I sent a couple of my assassins. Later on, I received a notification saying they were successful in saving the convoy, that the convoy reached home, and that I received my money. However, when I checked the accounting book, it still said "Attacked." I've searched for any answers in the net, and I found that a lot of gamers experienced the bug too, and that no fix or patch was available. Furthermore, I found out that the full use of all convoys was required in a trophy or achievement, which means the bug messed up more parts of the game than I thought.