It’s possible to keep a copy of your contacts, ... on the iPad:
You just have to enable it before signing out of the old ID.
After signing in with the new ID, you’ll have to merge the information with iCloud.
Images will be removed, though, so you’ll have to save them somewhere else, in an app, or online storage, or on your computer, e.g.
Documents in iCloud Drive will disappear as well. If you have another app that will work with the files, save them there.
If there’s something else you’d like to keep on the iPad, there might be a way to save it somewhere else but in iCloud.