Can't believe that you lost Barbas and was surprised to read that his wandering is a known issue... I had him follow me around for a few days. He was nearly ALWAYS right up my characters caboose. His invincibility came in handy while I got my destruction up. I've seen him kill both a giant and dragon. Him & Lydia got into a fight once in some cave & I had to reload. He accepted Lydia's yield so he didn't kill her, but she refused to stop attacking him. If I don't see Lydia for a while, I wonder if something killed her (not likely but possible), if I didn't see Barbas for a while - I wondered what he may have killed. His benefits barely outweighed his annoyances. He bumped me all the time. He shoved me off a few cliffs. He constantly nudged me too close to bandits when I was sneaking as I readied my bow. More than once, he bumped me as I was talking to vendors and the little "x" target that was aligned for "talk to...", ended up getting moved just enough to steal something on accident. Lydia often traps me in a room, or where I can't turn around in a narrow hall - Barbas just made it worse. You can't tell Barbas to "wait here" like most followers (even Meeko and the stray dog) & he knocked over stuff in the houses ALL THE TIME. If that wasn't enough, he barked non-stop. That sound, even though not literally heard in about two weeks - is burned into my soul forever. I had to send him home, I just couldn't stand the barking and constant nudging. I read up and found that if I ever want to spend more time with him, like to finish the quest - I will have to go to the shrine to reunite with him.
He did get "lost" a few times, and I found that he was actually just "stuck" - ramming his little body & head into some small ledge/step or stuck behind a pot. Loading another area usually helped, but I do recall at least once that it didn't. Did you back-step and check where you saw him last? I wonder if he is like most followers - where he may just go back to his "home" (shrine) after 3 days? My gut says no, because he isn't "waiting". Did you check the shrine just for fun? May be you nerves took over just long enough to dismiss him
. I bet he's somewhere...I really did loose him in a dwemer ruin once and he was just air-walking into a wall or something. I thought I'd have to reload, I always check to make sure my follower(s) is/are with me when it loads a new area so I had fairly prompt notice that he was MIA. Oh! Another time he didn't follow through a loading screen, he was very stuck in a falmer tent-thing. I don't think he knows how to turn around. Sounds like you've been all over the place since the last sighting so it could be pretty hard to find him...
Good luck!