You (almost certainly) couldn't save the company anyway
Unless you have concrete evidence that your leaving would cause likely and significant harm to others (as opposed to a vague feeling that the company can't function without you), then not only is it not wrong to leave during a "crisis", but you couldn't save the company by staying. It's common to feel like you're irreplaceable, but that's almost never true. And a company that's poorly managed will always be in a state of crisis. That does not oblige you to stay forever.
When is it wrong to leave during a crisis?
- If your leaving will truly jeopardize peoples' health, safety, or lives, then it is wrong for you to leave.
- If your leaving will devastate others financially and your staying does not cause more harm than your leaving would, then it is wrong for you to
You'll know if you're in either category. #1 would be critical care healthcare professionals, security professionals, first responders, police officers, and military personnel--people who often cannot go on strike or stop working without warning precisely for this reason: peoples' lives depend on them. #2 would be if you are a C-suite executive in a corporation; you probably shouldn't just up and leave, or you could (potentially) tank the company and mess up a lot of peoples' lives. Though even here its far less likely that you'll actually truly harm others than if case #1 applies to you.
If neither of these applies to you, then generally speaking you're not harming anyone by leaving, even during a crisis.
NOTE: in #1 and #2, "wrong for you to leave" means wrong for you to leave as long as doing so will cause the indicated harm; it does not oblige you to remain forever--it just requires you to be more deliberate about your timing.
At the end of the day however, you have the best information about your situation and must make the final assessment.