For example, if the company needs 8 fewer people to install and set up servers, but 10 more people to work on robust automated code deployments to support business growth, and both jobs need Unix skills.
Hence, the setting-up-servers department budget shows cost savings, the overall technology budget grows by 2 employees instead of by 10, and business growth means overall profit increases.
The job of the people is to translate the business requirements into stuff actually happening, and that doesn’t go away with cloud. If anything you need to do more of it (someone has to take care of auto-scaling, a thing that wasn’t possible in your legacy DC, for example). The worst thing you can do is sack the people then realize you need consultants at 5x the cost to do anything now...
Perhaps saying something like, "Are you sure the cost savings are really there, and you won't face unexpected hidden costs in the future? I have experience with X,Y,Z, and we found that while the cloud is optimized for x64 deployment, we had hidden costs A, B, C, crop up after 9 months."
As it is, it's only added noise and made you look bad.
Perhaps using http://www.paulgraham.com/disagree.html and avoid dismissing the content because you don't like the way they said it (DH2, responding to tone).
Those will remain where they are and, eventually be ported or replaced (or kept alive - IBM mainframes have been legacy-friendly for over 50 years now) by newer systems as they are phased out.
They're going to have tangential skills to the new platform.
Get your network team to learn all about VPCs and networks and security groups and peering and VPNs, train them to be your in-house experts to deal with changes and expansions and to help trouble-shoot issues.
Chances are you're still going to have systems, your systems engineers can be repurposed to better tie in your monitoring tools, your security tools, etc. You're going to need authentication and identity management, and probably have internal people handling it.
If they're motivated to keep their jobs, all it should cost you is a $5-20K/head in training.
That's peanuts compared to the turmoil of everyone thinking they're going to lose their jobs, or the costs of hiring new people w/ pre-existing cloud skills. It is cheaper than the stop-gap of paying outside consultants till you can bring in the interior staff. Also, these people _know_ your existing systems. They know your business logic, they know what needs to be up and they know what can't break on Thanksgiving weekend. That is valuable knowledge that is a hidden cost in rehiring the work force.
You're going to find new challenges in the new system. If your employees are willing to transition, then transition them. It is your best bet.
If you have a subset of employees that can't/refuse to transition, put them on performance improvement plans. No rumor mill - if you're on a PiP you need to shape up or get out; if you're not on a PiP keep doing well, your job is safe.