Only three switches in the pressurization panel are AC: engine bleeds, and isolation valve, and they will stay where they were, which is normally open in flight for bleed air. The pack valves are DC, so they'll continue to work. When all AC power is intrupted to the AUTO system, it automatically changes to STBY which will continue to pressurize the airplane.
In the meantime, according to the checklist attempts are made to restore AC power. If unable to engage ENG driven GENs, you might be able to start the APU, and then it's almost normal operation.
If not, you'll land on STBY system, and prompted by AUTO FAIL light you'll do that checklist, position the switch to STBY to get rid of the AUTO FAIL light, and continue with the checklist which will look after your pressurization situation. The AC/DC STBY busses continue to be powered by BAT bus and static inverter. Upon landing, as any emergency landing, the FO will do the recall items at 60 kts, one of which is to select STBY on Bat to allow for power transfer to STBY busses on the ground. Just remember that with no AC system, the AP will stay engaged, but it won't work. Hope this helps.