Create a new project, and transfer all of the data from the old demo file into the new project file. Everything will be there.
One downside, though, is that RPG Maker VX Ace will become stupid and won't let you view the graphics files. This has happened to me with some Ace games I downloaded. They let me check out the music used, but not the graphics. That may be your only problem, but you can easily get graphics back.
I would give this game a try, but the only download link I have found on this page is broken. Where can I download the demo? The main post should also describe the game more than like "Coming soon". If you have dropped the project, write that, do not leave everything without update, because it is disappointing.
suspended on twitter for calling an ahole an ahole & appealing the tweet; furious at myself for being even slightly upset with my suspension: oh no, you've been temporarily banned from hell. GET OVER IT, me.