Vacuum T&B's are kinda rare these days, but they are a reliable instrument. There's lots to be said for air-driven over electric gyros as far as reliability goes.
Of course, as you've already alluded to it (but just to reiterate for others) it's a good idea to have a mixed bag of power sources for gyros for redundancy. The most common being air driven horizon and DG, and electric T&B.
About 25 years ago had to descend thru a 4K-foot undercast using a vacuum T&B in my old Aeronca. I'd fallen
for a "current" observation that was made by a wx man who apparently never really looked out the window and ended up trapped on top over BHM at sundown in a non-electric airplane. My hand-held got me a descent clearance from approach after making a "turn for identification". You know how long it takes to descend thru 4,000' of cloud on AS/needle/ball? Almost 24 hours! 
I'd entered it at about 7K and broke out around 3K.I hope I never have to do it in rough air! (When I landed, I was instructed to call the TRACON facility. I expected to end up filling out all sorts of paperwork and maybe a scolding. Turned out the controller who worked me owned a similar Aeronca and he wanted to talk to me about what it was like. Whew.
