They are normally connected using check valves so that either can run all the instruments. If one fails, the vacuum from the other assumes the load for everything.
On single engine airplanes such as the T210, they may be equipped with two separate vacuum pumps connected that way also.
Anyone who does a lot of IFR will put in an electric attitude indicator on the left panel for a backup.
After reading the comments about his log book, it is obvious he was over his head.
I would not ride with a pilot who has not logged at least practice IFR in the last month.
Could you go without driving a car for 6 months and then jump into LosAngeles traffic in a race car?
Sounds to me like he didn't realize the left AI had gone until it was too late. I'm surprised that a pilot flying commercial for-profit wouldn't be much more current with IFR. It also raises an interesting point: presumably he was flying with constant-speed props -- with fixed-pitch props, he would have easily heard the engine speed-up when he started to pitch down.