First of all, you're looking at things wrong. You're running Exchange and other services on your server as well as Active Directory and DNS. You're doing it wrong. You really want Domain Controllers to only run Active Directory and DNS. You'll run into serious performance issues down the road if you get a medium number of mailboxes in Exchange and it runs on a DC.
That being said, downtime is a real issue. Is your boss OK with users not being able to log in, access file shares, access other SSO technologies that you might leverage for the hours that it will take to do a restore? If you have two DCs (or more) and you have exchange and file services running on separate servers like you should be, then this becomes a very real problem.
As it is, it seems like you already have all of your eggs in one basket, which is a really really bad position to be in. You should be pushing for a dedicated Exchange server, a 2nd DC, and possibly a file/print server. This, of course, depends on the number of users that you have. Even if you do keep Exchange and any file\print services on your existing DC, if it goes down, your network users won't even be able to log in to their machines to even have basic Internet access.
Finally, seizing the FSMO roles is trivial. As long as both DCs are Global Catalogs, you don't even really have to transfer the roles if you're going to be fixing the downed server immediately anyway.
You're already in a bad position. You should be working towards rectifying it by adding the additional infrastructure that you need to eliminate all-or-nothing downtime, not throwing your hands in the air and saying "well we're pretty much screwed anyway."
Moving a VM is as simple as exporting using the Hyper-V manager, moving the files to the new server, and importing the VM using Hyper-V manager. There are a quite a few really good instructions on how to do this online.
(I'm assuming you're not moving the VM between clustered hosts, because if you were this wouldn't even be a question.)
The only thing when moving domain controllers is to NEVER TURN ON TWO COPIES, and NEVER TURN ON AN OUTDATED COPY. As soon as you move the VM and start it up, DELETE THE OLD COPY.
Best Answer
Creating a single, clustered Domain Controller isn't creating highly available AD services. It's creating a highly available VM, regardless of the services that VM is serving. If you lose the VM (OS failure, data corruption, etc.) then you've lost the services that VM was serving, so those services were not highly available to begin with.
Don't confuse a clustered, highly available VM with a clustered, highly available service. A clustered, highly available VM makes the VM highly available and indirectly makes the services on the VM highly available BUT only so long as the VM itself is up and running. if the VM itself is down, so are the services it provides. Clustered VM's protect against HOST failures, not VM or service level failures.
The proper course of action would be to create two Domain Controllers. Place them where you wish and cluster them if you want to. If it were me, I'd create two and place them as you've suggested (one DC on each host) and I'd cluster them as well. There's no reason to have one of them be unavailable if one of the hosts goes down. Clustering them allows both to continue serving clients regardless of which host is up or down.