Failure Indicator comes on and pressure gauge drops to 0

That is telling you your oil pump is not pumping no oil pressure but since it's not tapping or making any kind of noise at 70 - 80 mph I would say you have a bad oil pressure gauge or sensor they goes to gauge.

I would get it to a specialist before driving it again. If the oil pump is going bad, you could end up with a huge engine rebuild bill

I would have it towed to an authorized mechanic. Don't take chances. Things to remember: Always check the oil at full operating temperature? When you start the car, is there oil pressure? Does the engine rattle when it first starts?

Oil is the life blood of you vehicle. Bouncing pressure on the gauge and low readings can occur for a host of reasons. Bad sensors, older engines, etc. If you warning light is coming on under speed I would get the problem professionally diagnosed and fix immediately .

Own a 2004 996 Turbo Cabriolet with 65000 miles. The first thing I would do is start the car and bring it to operating temp. and check oil level. Second, I would check wire connection at oil sending unit. Third I would replace oil sending unit, which if it read low pressure would trigger an " oil failure light " on your dashboard. Oil pumps do fail but very rare, and usually it would make some sort of noise and the vehicle engine temperature would increase substantially. Faulty oil sending units are not uncommon on these vehicles once you start putting some miles on them, I am assuming that you have maintained your car oil and filter, dirty oil can block the sender and produce faulty reading. Replacing the sending unit is a bit of a pain in the neck but can be done at home if you have some mechanical knowledge. You tube has several videos to help you. Good luck.