How to get my minecraft save back?

Try opening up your launcher, click the "Edit Profile Button" at the bottom left, and click the "Open Game Dir" button on the bottom there. This should open up your.minecraft folder. Once you're there, click on the "saves" folder and look for the file with the name of your world. Once you've done that, you might want to copy your world folder to something like a hard drive to make sure that this can be easily reversed if it happens again. After that, to get it to show up ingame, you need to:
1. Create a new world ingame Minecraft, you can name it the name of the lost one because this world is going to turn into your lost one.
2. Get to your "saves" in.minecraft as shown above
3. Open up the file of your lost world
4. Copy everything there into the folder of the new world that you created in Step 1.
5. Open up Minecraft, and if it worked you will be right where you left off in your iron farm.

I'm sorry, David. Your iron… Your iron farm's gone. Unless your dad ninja-stole it via a flash drive.

Copy and paste this path into your address bar in an explorer window replacing (name) with your Windows account name, clicking on.minecraft and going into saves:
C:\Users\(name)\AppData\Roaming\

It may also be inside your recycle bin.
Or it's been corrupted.