Great answers, here's 2 another ideas, to add to the list:
- A roll-back plan.
Before the launch, you should have all the members of the team agree on a roll-back plan.
That would include storing a precise snapshot of the existing system somewhere, as well as who is in charge for the roll back, who gets to make the decision and how to contact all relevant parties.
You may also want to decide beforehand on criteria (besides for management disapproval) of when a roll-back would be warranted.
- A staggered rollout.
If you can first roll it out to a small percent of the users, that would enable management to decide if they like it without having to worry about a full roll-back.
For web-based roll outs, you may want to put some system in place (cookies or a URL parameter) that would ensure that management will always see the new version.
These concepts only work if you plan them in advance. They are not fire-fighting methods, post-facto.