I only delete PC's from AD if there is a conflict, ie renamed PC and someone forgot and then made a dup. But then sometimes they need to be moved to workgroup then back to domain. I don't know of any other way.
And for the image thing we build new images with each new model of pc because of HAL issues. We configure them just enough tto deploy without joining the domain. When deployed we run a SID changing tool then join the domain. for people with alot of files, we clone their drives, put a fresh image on. Then copy their cloned drive either on the network or local. Then they can access all their files and add them as they want. I'm using Acronis but it allows you to look at the backup like its a giant folder so it's easy for users to get their files.