In an extremely rare case where a certain electrical bus fails, you might lose most of your fuel gauges and you would probably have both (or more) fuel burned counters to use instead of most fuel quantity gauges. It can depend on the enroute and destination weather. A certain circuit breaker popping could mean the loss of all fuel gauges.
If a different elec. bus fails on our plane (and COM book procedure does no good), we would lose all fire detection and protection for both engines and APU. In good weather, this would also cause the loss of the standby artificial horizon and would be no problem, but the fact that fire protection is lost would be a good reason to land soon.
I know a guy who was headed from St. Louis to the west coast. It was his first flight as MD-80 Captain. He and the Check Airman noticed enroute that when adding fuel remaining to the fuel burned figures, it did not nearly add up to the original dispatch fuel load. They diverted to Phoenix. After landing, the aft flight attendant said that she could smell fuel. They knew it was best to stop and told the passengers to exit down the main stairway onto a taxiway. The firemen showed up and standing by an engine which had the leak, the fuel puddle was so deep that a fireman's boots were almost submerged in jet fuel-quite a leak gushing from the right engine nacelle.
