Regardless of which happens, resetting keychain password would help you access Keychain again. Probably you are just prompted to do that at startup after Mac admin password reset, such as on Yosemite, or constantly asked to enter the keychain password after Mac login. Since the keychain is still protected with the old administrator password, there would be no way to get back into it unless you could update keychain password or create new keychain.

No matter which method you use to reset administrator password on mac, it won't automatically update the password protecting the account's login keychain. How to Reset Keychain Password after Mac Password Change