Finding a Mediator for a Troubled Collaboration
See also III.i. Handling a Mathematical Divorce. A few mediated situations are described there which might be used as a warning towards bringing in a mediator in a more or less successful way. Some of the situations at least result in a published paper.
If anyone has a positive story with a successful mediation, please send me an email at sormanic at gmail and I can add it anonymously or in your own name.