Redundancy is always a good idea
But --- selling that concept to management that we are going to virtual desktop and, at the same time, keeping those servers and desktops around JUST IN CASE rather wrecks any business case. Management is not IT saavy to start with (well, at least in so far shipping jobs off to India) and will question one or the other. You won't get both. Now, in a small office (20 computers) you cannot justify virtualization but in a larger office (1700 systems) you cannot justify using both systems, it will be one or the other.
Again, I think virtualization is nifty and technically interesting. But that was Robert Oppenheimer's reaction to the Ulam/Teller design for the final Hydrogen Bomb too.
