Well the company will lose a nice person. So some one can accuse a person of bullying wreck their life for months and then waltz back into work.
Yes, just that, I'm afraid. To some extent, I think it just comes with the territory of being a manager, but it's shit when it happens.
I was in this situation once. An employee took out a grievance against me shortly after I had launched capability proceedings against her. The irony was, I had bent over backwards to help her sort out her performance! She made all sorts of wild, viscious allegations against me and managed to stretch out the process for months, but ultimately she failed to substantiate any of her claims, because obviously, there wasn't any evidence. Although I knew there was no way her complaint would be upheld, it was one of the most stressful periods of my career, and I really struggled to cope. One of the worst parts was the unfairness of it all. She was spreading all sorts of malicious rumours about me, to anyone who would listen, but as the manager, I could only give my side of the story to the investigating panel. It felt horribly unfair, but that's just the way it is.
Eventually, the grievance wasn't upheld, and it was found to be malicious. She came back to work, and I had to line manage her again. I didn't even want to be in the same room as her, but you just have to be professional and get on with it. Your friend is the manager, and that's her role.
Huge sympathy though. It sucks!