Quick questions on crisis management

What do you do when you have to deal with a mismanaged project? Here are the constraints:

1. You cannot rewrite the application because client is still strict with timelines
2. Unit testing was not done properly and a bunch of requirements were never coded
3. While fixing defects, more and more defects are getting introduced
4. Resources are not competent enough to handle all the technical difficulties and few of the good ones become heroes are are over worked
5. After being mismanaged, the senior management suggest to go on a 24x7 repair plan and completely over seeing their responsibility in having the project in this situation in the first place. This has resulted in people getting overworked, and resulting in stress