The reason the bug is a crisis situation is that there is nobody available to fix it: you need to document this and work with your manager to ensure that there are always developer resources available in case something like this occurs again. Note that this isn't a case of laying blame - if the entire project was run on an overly tight timeline, it's quite possible that your team wasn't able to access the part of the system with the bug until the last day. Or other factors could have intervened: hardware failures, interaction with third parties... in my experience nobody wants to deliver substandard software, but that doesn't mean that circumstances allow everyone to work to the standard they'd like.
