I was wondering if its even possible to play the audio file from the sd card ( whenever the data point exceeds a certain value) while continuously writing the sensor data to the card.
So, that library has a file open on the SD card, using 512+ bytes of SRAM. Do you have enough SRAM to open a second file, using another 512+ bytes of SRAM?
How quickly does that library use up the 512 bytes that it reads each time? How often will you fill up the 512 byte buffer that you will be using to write to the file?
How important is it that the audio play glitch-free (that is, with no delays caused by you writing to the card when it needs to read from the card?
The only way to really know is to try it.