Do you mean a completely manual workflow where you copy dependencies into the vendor dir by hand and then they are part of your project? If so, you back them up with your project backups and they also go into your repos history?

Otherwise, I would be interested, how you "copy" a git repo that goes into your vendor dir. Where you put the list of repos that need to get copied. Which command you run to copy them all. How you handle it if they have sub-dependencies and how those get installed in your workflow.