I have been flying my IV-P for almost 5 years, from
the beginning I installed a very expensive (only thing
available then) backup electrical AI (BF Goodrich)
which has its own battery and sits in a different
buss. All my insttuments are electric and I got rid of
the vacuum stuff. So with a backup alternator the only
system that is single is the battery and I fly with a
garmin 390 which has an artificial AI and its own
battery.
You need redundacy, I still remember the son of some
government guy who bit the dust in Lake Pontchartain
when his old vacuum pump gave out, the company had to
go out of business due to the suit, very unjust, the
public believes that vacuum pumps are to last
forever... get a backup system and fly safely