In the event you have deleted a project from "My Projects" under the "Create", this will also delete the project from C:\Users\User\Documents\My Games\Core\Saved\Maps (default path where "Users" and "User" are unique to your PC). Also, please note that deleting a project on your PC does not remove it from the Core platform if it has been published (publicly or unlisted).
However, the good news is that you may be able to recover the deleted project from your autosaves (albeit, with a little leg work). To do this, please follow the steps below:
1. Go into the Core client and create a new project (name it whatever you like, but remember the name). Exit the project and Core client.
2. Find the folder containing your previous autosave in C:\Users\User\Documents\My Games\Core\Saved\Autosaves\Standard
3. The folder will look like this but WILL NOT be the same: 9A53F00303EB3CE468617DC25EEC244C_backup
4. Open that folder
5. Copy all of the contents (All folders, all of the .pbt files) using Ctrl+C
6. Go to C:\Users\User\Documents\My Games\Core\Saved\Maps and find the folder with the name of the new project you created in the Core client
7. Open that folder
8. Paste all of the contents to that folder using Ctrl+V
9. Open Core and then open the new project you created previously - you should now have everything available in the new project
If you have multiple _backup files, repeat the process for each _backup file until you locate the content/game/template you are looking for. Since they are new projects each time, there's no risk of overwrite, etc.
10. Publish the project as you would any other content.