Hi i was wondering if there's any way to download an existing game made with AGS in the AGS editor even when the .dta file isn't there. In other words, I want to be able to conver the view files back into an editable form.
No, and that's intentional.
Most AGSers don't want other people to "borrow" thier work without permission, so, only if an author of a game wants to publicly release all thier files, then no, there's no way to see thier game's source code.
However, there's still some generous authors that have released thier game's original source files so other people and learn from, and/or use parts of it in thier own games. However, it would still be nice to contact said author if you plan on using some of thier work in your own game or to at least give them credit.
On the AGS site from the DownLoad page, you can download a Demo game that has the complete source-files for users to view how things work.
Another site that comes to mind is the website of the generous "Junc", over at:
http://www.juncmodule.com/mt/archives/cat_games.html
Some other members here can probably give more examples of AGS games with the source-files available.