Single Player in Toribash has always been used for the replay makers mainly to pull off cool moves and show them off to others. I believe it has been very successful in that particular aspect, still holding a competitive feel without actually face to face fighting someone. And I personally, have been satisfied with that.
However, recently I took quite the trip through Europe and some of the world. And while sitting in the airports with their atrocity of an Internet service, removed from Multi Player entirely. I couldn't help but be rather disappointed with the variety Single Player had to offer. Potentially, no variety or challenge whatsoever when you step away from the Replay Making side of Single Player.
Personally, I would like to stay on a realistic stand point. Remove yourselves from an AI concept, and think what else can be done? What about challenges of varying difficulty? Steam is rather light on achievements nowadays, why not throw in more revolving around the Single Player side of things? Breaking off a certain number of limbs from Uke in a certain mod, beating Uke in a race?
How about instead of mods like obstacle courses being kept in a backlog of mods, they are set aside to complete in Single Player for an achievement, or perhaps even entirely new mods are made for this purpose? This could in fact be entirely recreational or to kill time with no Internet, like me when I was stuck in those airports.
Maybe think about other possibilities other then simply the combat aspect of TB, although it does not hurt to be explored further. Of course, away from AI standards. Toribash is a unique game, with tons of ways to shape a Single Player experience. I'm sure you guys can think of something more without getting stuck when it comes to AI.