This is a question about data saving during a power failure on a µR with an SD memory card (/EM1). If a power failure occurs while saving to the SD memory card, can the data just before the power failure be saved to the card?

Yes. Data up to the moment just before the power failure is saved to the card. During a power failure the μR SD memory card (/EM1) stops, but the data to be written to the SD memory card is saved in buffer memory.
When the power is restored, the data in the buffer memory is then written to the SD memory card as a file for data before the power failure. Thereafter, a new data file is started.