You can reset brushes to their default profiles and settings by clicking Reset Brushes. The default brushes will now be used the next time you select these operations.
You can undo as many strokes as defined in the Undo category of the Preferences window.
You can erase the strokes you paint by painting over them with the Erase brush. When you erase, you remove the color from the painted pixels, revealing the last saved texture.
To set the background texture to erase to, turn off Update on Stroke and click Save Textures. Flooding with the operation set to Erase restores the texture to its last saved version. You cannot erase when Update on Stroke is turned on, since the texture is constantly saved.
In the Tool Settings for the 3D Paint Tool, you can use the Set Erase Image button to set the current paint layer as the one to erase back to.
Example of using Set Erase Image