If you manage to corrupt a disk (or slice), no worries. You can easily repair the damage yourself by reloading a fresh copy of the default disk image. You will of course lose anything you have stored on that disk; it is a good idea to store only data that can be easily recreated, or backup your data offsite.
On your experiment status page, you can click on a node in the topology diagram, then click on "Reload" from the context menu. You can also reload a node (or a set of nodes) on the "List View" tab on the status page.