PC-12 pilot reported a standby bus failure caused numerous system failures and diversion to a nearby airport.

Narrative

IFR flight from ZZZ1 to ZZZ2; ZZZ3 was the filed alternate. We departed ZZZ1 at XA:30z. 3/4's into the flight; we were beginning our initial descent into ZZZ2. Level at 16;000 ft; the CAS alert system went off. Display unit 3 had failed. We communicated with ATC to stay high while we worked out the issue. Upon realizing what truly had failed; and after running all checklists that applied; we [requested priority handling] with ATC. Our standby bus had failed; along with everything tied that bus. The first noticeable changes were:Failure: Standby bus ' loss of DU 3 ' LH PFD controller fail ' LH audio control panel fail ' GPS1 fail ' Pilot to pilot communication fail ' TSC and CCD failureWorking with ATC; we found an airport that had improving conditions. ZZZ. Using ground navigational information; and what we had available in the aircraft; we attempted the localizer approach for runway XX. We broke out of the clouds at 1;000ft MSL and continued for safe landing.This was an [priority handling] event because of a resource restricting and environmental degrading failure in IFR conditions.In addition; the Standby bus failure checklist in the QRH seemed inadequate for the task at hand. There were more issues revealed than what was covered by the checklist. Such as: ' Minimal MFD control ' Needing to dump cabin pressure for safe control of the CPCS