A Mule app can easily be rolled back to a prior version of the app if there are one or more prior versions of the app in the Mule repository.
Let's say the repository has the following for your app:
When a new version of the app is deployed to Mule, a new snapshot will be created in the repository, such as SNAPSHOT-04. If there is some problem with the new version of the app, you will undeploy the new snapshot and then deploy the prior snapshot.
Undeploy the application
You can also check this on the command line by signing into the Mule server, and listing the contents of the mule_home/jvm_name/apps/ directory (Linux). There shouldn't be any files or directories listed for the app that was undeployed. If there is a app_name.anchor.txt file, delete the app_name.anchor.txt file, to force the application to be undeployed. This must be done with Mule running.
Deploy the prior version of the application