>Then, Mr. Wolf has a glorious idea and rans off north. Says "I'm going to look if the robbers left anything on their trail." People tell him not to, since they just left, but he does anyway. I haven't even removed their pieces yet, so I have to play them like they're still there - the lone wolf gets spotted. In the end, the group is overwhelmed.
Ok, at this point he starts being a retarded player, not a lone-wolf. So far he'd chose to stay behind and not participate..fine, it's shitty but understandable. I'd still much rather have a lone-wolf who is MINIMALLY a ranger of sorts, so they can be a part of a battle even if from far. Much like a sniper.
Now, I won't say that this is what you SHOULD have done, but it's how I would have decided to work it out. After Mr. Wolf gets spotted, the 'group' isn't overwhelmed. He is. If he failed his roll and the robbers spot him, have the 'fail' not happen right away, but after he'd been following them for a while. Then he gets captured.
The rest of the party finds out later and decide (or not) if they wanna go rescue him.
Of course, if Lone Wolf wants to try to escape, by all means allow him, but make it clear that he's outnumbered and there's a big possibility that he's killed in an escape attempt.
Have the party HELP him and, in-game, have him explained how they won't always be there for him if he continues. (that'd be up to the players, but I'm sure they'll understand where you're getting at and play along)