Password changes: You had months of time to cause all kinds of damage with your password and you didn't. You are leaving because your contract ended just in the normal manner, so nobody would expect that you would start causing damage now. You should (during the time they pay you) probably create a list of all your company passwords and hand it over to them; they can then decide whether to delete all accounts immediately, take their time to delete them, at least until they verified that they can access everything, or maybe even leave them for a short time in case they pay you for another week to fix some small problems.
What would be absolutely awful: If you delete your passwords, and it turns out that you were the only one with access to something.
It is usually logged who connects to some server, and where from. If someone messed up, that wouldn't be done from your account. If someone says "I'm stupid and probably mess up, so I use joshuaty's account and blame him if it goes wrong", well, that's an attitude that may put the person into jail in the worst case, and at least open them up to a libel case.
PS. People have passwords related to the company they are working for that are not controlled by the company but by a third party. For example if a company product uses a third party service, then someone must have registered an account with a password for that third party service. That kind of password cannot just be changed by the company.