An environment here means a development, QA or production environment. This environment could consists of one or more than one Virtual DataPort servers. And as you know each VDP Server can have more than one schemas like schema A, schema B etc. which is basically called Virtual Databases in Denodo.
Now, regarding the rollbacks in Solution Manager, only if the current deployment fails, and if you have the option checked, Solution manager will automatically rollback to the last stable state.
So, lets say if your last stable state(State B) was only changes with Schema B. And prior to that your last stable state(State A) was only changes with Schema A. That would also mean that **State B** would have the changes of Schema A and Schema B both.
So now, when the current deployment fails, Solution Manager will rollback to the last stable state that is the State B. Which will contain the changes from Schema A and Schema B as well.
You as a user, cannot choose to rollback to any stable state, it will automatically rollback to the LAST stable state.
Hope this clarifys the situation!