Quote Originally Posted by Cuchulainn
What happened to Zargan after Nibelheim? Did Shin-Ra kill him to keep him quiet?
He searched Nibelheim for survivors, but only found Tifa after he saw Cloud, Zack and the other survivors being rounded up by Hojo. He used curative magic to keep her alive till he got her to Midgar, where he found a doctor. He then went into hiding.

This is revealed in the hidden letter in Tifa's piano.