via make.wordpress.org => original post link
While it is a rare occurrence, updating plugins and themes can fail in such a way that leaves the old plugin/theme non-functional, and may leave users with a broken site. #51857 intends to add the ability for core to “rollback” to the previously installed version of a plugin/theme when such a failure occurs.
Over 19 months of development and testing has gone into this feature, primarily by @costdev, @pbiron, and myself (@afragen). Several different solutions and they have led us to the current PR2225.
It was determined that copying the current plugin to an alternate location and in the event of an update failure, copying it back into wp-content/plugins, would be the least resource intensive method. This does require one additional plugin copying operation and two if there is a update failure.