As others have pointed out don't update your app of you want to retain the original functionality - as long as you don't mind keeping possible bugs and other issues that have been fixed in later versions.

Generally all uploads not manually deleted by the developer stays on the App and Play stores but users don't have access to them.

It seems like there is an apk of an old version available on some site that someone has uploaded for people to use. That is also an option although I suspect not legal if the uploads are not by the developer.