Did you unplug the wire(s) before unscrewing the switch, or barring that, hold the center of the switch to prevent it moving while using a regular wrench on the fixture?
If not, it's entirely possible that the wire(s) got cut or twisted up in such a way that things are gounding someplace other than through the switch.
The switches are nothing more than ground contacts with spring loaded plungers to allow the contact to be broken when the plunger is depressed. If depressing the plunger doesn't break continuity, the wire is likely shorting to the chassis or there's something radically wrong with the spring and end clip of the switch. (very unlikely though as it's more apt to actually fall apart or not allow continuity as opposed to the other way around)
If not, it's entirely possible that the wire(s) got cut or twisted up in such a way that things are gounding someplace other than through the switch.
The switches are nothing more than ground contacts with spring loaded plungers to allow the contact to be broken when the plunger is depressed. If depressing the plunger doesn't break continuity, the wire is likely shorting to the chassis or there's something radically wrong with the spring and end clip of the switch. (very unlikely though as it's more apt to actually fall apart or not allow continuity as opposed to the other way around)
