Decode function in SQL Server
You should be able to turn the decode into a case:

UPDATE
  [SCHEMA].TLS_FAC_PRC_ONG
SET
  FPO_RID_OWNER = CASE FPO_RID_OUTSTANDNG
                    WHEN 'NONE' THEN FPO_PID_FACILITY
                    WHEN NULL THEN FPO_PID_FACILITY
                    ELSE FPO_RID_OUTSTANDNG
  FPO_CDE_OWNER = CASE FPO_RID_OUTSTANDNG
                    WHEN 'NONE' THEN 'FAC'
                    WHEN NULL THEN 'FAC'
                    ELSE 'OST'
                  END