Your immediate manager is supposed to be protect your from that. They're the ones who are hosed when everyone burns out and quits.
On the flip side, if people don't quit and you succeed in delivering the project, your client manager will claim the credit. And that level of output becomes the new expectation for your team.
On the flip side, if people don't quit and you succeed in delivering the project, your client manager will claim the credit. And that level of output becomes the new expectation for your team.