If a power failure occurs while reports are being created, is the report up to the failure created?

No, but the creation of the report restarts after recovery from the power failure. The operation is different depending on whether the recovery time is before or after the report creation time has elapsed. For details, see "Special Data Handling " in section 1.8, "Computation and Report Function (/M1 and /PM1 Options) " of the user's manual. (Note: measured data files are created up to the power failure.)
DX1000 user's manual
DX2000 user's manual