I agree that the clone is a good option here as is the V2V.
One very important point to remember - Microsoft doesn't support virtual machine snapshots of any kind with Exchange 2010 (or 2013 for that matter). You can actually cause issues with your databases if the snapshot isn't Exchange aware. Regular snapshots in vSphere can be OS aware but are not aware down to the application level. Some virtual machine backup products use Exchange aware VSS integrated snapshots but you should talk to them to make sure whether they are truly supported.
I know this info doesn't help for your current situation but is definitely good to know for the future.
Best of luck getting this snapshot deleted. Feel free to post back if you run into any trouble.
Matt