B will not be executed. The microflow will continue with the next iteration of the loop.
As Johan said, B is not executed, unless the activity that was rollbacked had a custom error handler. In this case your error handling routine should perform the necessary cleanup actions.
Probably not, activity A is rolled back so activity B will not be executed.
The 'continue' property on the loop will execute the next loop and if activity A is executed succesfully activity B will be executed that time. If not, then activity A is rolled back so activity B will not be executed