I was alerted to a failure to pressurize in a King Air by a packet of potato chips that burst going through 16,000' for a final FL210. IIRC the only warning is a yellow light on the annunciator panel. Always carry an unopened packet of potato chips with you, it may save your life. I've also flown the 421, max FL260.
I am a 421C Owner Pilot and first, my condolences to the Pilots family. I'm so sorry to read we have lost another pilot, I just hate reading these reports. The mystery: To file and fly a 421C at 27,000' - FL 270 - means the plane would have to be very tight, as if it was not, the small amount of Preasurization available to all 421 drivers, would not give much of a breathable enviroment at that Flight Level. As the article mentions, most 421 pilots fly in the lower flight levels, mainly because most 421s do not pump up to the max differntial as they get older. I generally don't fly mine over 24,000' (FL 240) for that very reason, even then, I would be wearing an oxygen mask, just for safety, and always if single pilot over FL240.
Is the regulatory ceiling lower because of the relatively high age of the aircraft?
The regulation is that above FL 280 aircraft and operators must me certified to RVSM standards which is reduced vertical separation minimum. It has nothing to do with the aging aircraft other than expense to re-equip an older piston twin to meet the requirement. The RVSM standards allow a continued 1,000 foot vertical separation above FL 280 to and including FL 410. Above that it goes back to the 2,000 foot separation minimum.