It's gone not because the game file deleted itself, but because your virus scanner removed it from your computer because it doesn't trust the engine. If you can look around your computer and find out the name of your virus blocker, you can use the name to search online how to turn it off/make it stop suspecting certain files ^^.
If you're a Kickstarter/Patreon backer, would you mind messaging us on those sites for help getting rewards? The keys were all sent, it could be in your trash or spam, but we can resend them if we know your backer details info.