The answer is quite positive because there're ways for you to recover macOS Mojave keynote files. One is to restore lost Keynote files from Time Machine backup; the other is to use a Mac Keynote file recovery program.
There're many Mac Keynote recovery programs in the market, Recoverit (IS) for Mac is one of the best options for you to get back lost Keynote files.
The easy interface and powerful recovery of the program enables you to restore lost, deleted, formatted or even corrupted Keynote files from all Mac models, including Macbook Pro, iMac and Macbook Air and more. Except from Mac Keynote file recovery, you can recover files like videos, photos, audio files and document files from your Mac's hard drive, external hard drive, USB drive and other storage devices.
Recoverit (IS) for Mac offers you a trial version to scan your Mac and preview found Keynote files before recovery. Please download the right version according to your operating system. Below is a step-by-step on how to retrieve lost Keynote files on Mac. Windows users please take the same steps.
After successful downloading and installation, you then need to run this Keynote Data Recovery software on your Mac (macOS Mojave included).
Then the program window will detect and list all volumes on your Mac. Please select the one that contains your lost Keynote files and click the "Start" button to begin scanning.
Tips: The default scanning process needs a short time, if you want to get a deeper and better scanning result, you can select the "All-Around Recovery" option at the bottom of the interface after the quick scanning process.
When the scanning is finished, the found files will be displayed in the window with original names according to file structures. You can now preview the result and tick the files you want to recover. Finally, click "Recover" to restore them back to your Mac.
Things to Remember:
Normally if you have set Time Machine backup on your Mac and your lost Keynote files are contained in it, you can restore them from Time Machine.
You just need to go to the Time Machine menu and select the Enter Time Machine option and then open the folder that contains the lost Keynote files to restore them. If Time Machine doesn't help, you'll need a Data Recovery application then.