4.5 hours of a consultants billing rate can be much more than 10 hours of your regular hourly rate working a similar job. A good consultant will have a contract. The client saying I won't pay if XX happens doesn't mean anything unless it was in the contract.
Networking/spanning tree loops, arp table mismatch/corruption, the switches at the destination being misconfigured are all realistic problems that would result in downtime here. The normal way you do this is with live migration from hyper-v or vmotion from ESXI. If the initial migration is not successful, you just leave the server powered on while you address the issues. Once the VM has been migrated you can do whatever you want with the original server without worrying about downtime.
This reminds me so much of when I joined vmware in 2006. vmotion had already been around for a few years - but I believe this was the first release of vCenter with DRS.
A couple of months I joined, a room full of customers chewed us out for not publishing our vmotion compatibility tables. After 4 hours of chewing out - they then told us they reverse engineered the compatibility tables and reorganized their entire data center to conform to vmware vmotion. Then (of course) we worked with intel to make sure the compatibility matrix worked in the future.
I realized at that point that I joined the right company.
Networking/spanning tree loops, arp table mismatch/corruption, the switches at the destination being misconfigured are all realistic problems that would result in downtime here. The normal way you do this is with live migration from hyper-v or vmotion from ESXI. If the initial migration is not successful, you just leave the server powered on while you address the issues. Once the VM has been migrated you can do whatever you want with the original server without worrying about downtime.