I can't speak for all libertarians, but I consider myself a libertarian and I can make some observations about this whole situation..
1. Those customers who were stolen from will get to participate in the mother of all class-action lawsuits. The settlement will be outlandish. Juries hate huge corporations that screw the little guy, and the lawyers on both sides know it.
If you don't trust the class action to provide you with an equitable settlement, you can opt out and sue them individually. No doubt many lawyers are already lining up for the easy money here.
I've never known a libertarian who opposes the existence of a legal system.
2. So far, no one has produced evidence that the CEO knew about this or allowed it to happen. Putting him in prison would therefore be unjust. The article claimed that his sales quotas were excessive, but the only source for that is the same employees who knowingly defrauded their employer. Relying on their honesty seems like a bad idea.
What we know for sure is that he had sales targets for his salesmen, which is not unethical or unusual. We also know that the vast majority of Wells Fargo salesmen did not resort to fraud to hit those targets.
Even if the sales targets were high, the employees should either step up to the challenge, request a transfer out of sales, or resign. There are no excuses for defrauding your employer, and claiming "my job was too hard, so I lied!" is cause for termination.