What can a pilot do if an air traffic controller is incapacitated?
In theory, if the lone tower controller is incapacitated, the airport is no longer controlled and pilots should use the standard procedures for uncontrolled airports, i.e. making traffic calls on CTAF.

In the KLAS case, the pilots had every reason to expect the tower to be open, and rather than getting no response, they were getting unintelligible gibberish. As a result, their reactions varied.

If the situation had persisted, one of them would have notified Las Vegas Approach, who in turn would have started advising pilots of the uncontrolled field ("change to advisory" rather than "contact tower"), and everything would have proceeded fairly normally. Since it happened at night, traffic volumes were low enough that CTAF would have worked okay, which is probably why only one controller was on duty in the first place.

However, a supervisor was in the tower on break at the time, just not in the cab, so he was able to take over relatively quickly and resume normal operations before that actually happened.