I use Domain Mapping along with Pro Sites on my multisite. I works fine, when the user maps it's domain, and if they unsubscribe from their Pro subscription, they will loose their Domain Mapping. BUT, when they loose domain mapping, they also losse their domain linked to their blog, and then all the images they have uploaded when their blog had it's own domain, is still linked to their own domain.
For example: A blog names wuhu.blog.com maps it's domain to wuhu.com. When they loose domain mapping, all the images they uploaded when it was mapped, is still linking to the mapped domain.
Result: A lot of crashed images/blank images..