Hyper-V How to define “auto revert” to a snapshot after each reboot

There is a way to manually merge the snapshots. Here's the process in a nutshell:

1. Make a copy of the VHD and its corresponding AVHD files.
2. Rename the AVHD extension to VHD.
3. Write down the order of the disks from youngest to oldest (the oldest should be the root VHD). You can do this by looking at the last modified time stamp on the origional AVHD files, find the one that last changed. And find the last one that changed before it.
4. In the Hyper-V manager, open the Edit Disk wizard. Browse to the youngest VHD in the chain, then choose 'reconnect' to point to the next youngest (the one that came before).
5. Open the Edit Disk wizard a second time and merge.
6. Then repeat the process until you have only a single VHD.

See the source article here for more information.

In the future, you should move VMs around by exporting them and importing them. It's a lot safer to do. Microsoft has a nice blog about it here

Also, this is a great time to evaluate your backup methods. Hopefully you didn't lose anything this time, but what about next time?

The short answer is to delete each of the snapshots (The one from 1/2010 and 6/2012) and then shutdown your VM. Hyper-v will merge the AVHD files into the original parent VHD and you will have just the one VHD file at the end.

However ... there are a few things you need to be aware of.

1. Depending on how large your AVHD files are, the merge process may take quite a bit of time. I can see from your screenshot that the original snapshot was taken in January of 2010 so I'm sure the AVHD file from that snapshot may be quite large.
2. Do NOT turn on the VM until the merge is complete! The GUI interface will not provide you any status on that. You will need to look at the original VHD file size and date / time stamp to see when it stops changing.
3. If you have the time and space, I would highly recommend that you shutdown the VM and export it before deleting the snapshots just in case you encounter any kind of error. Store this in a safe place in case you need to "revert" back to it (by copying it back and doing and import).