As soon as Sephiroth takes the two eggs, the mother hadrosaur stands up and loudly trumpets at the boy. The creature leans forward in an attempt to swipe at the thief, but Sephiroth would be quick enough to get away before the mother can harm him. In addition, the boy would be lucky enough not to have her charge after him since the mother is more interested in perserving the rest of her clutch than search for two lost eggs.
If Sephiroth were to run to the East, he’d eventually come to a small hill which has another small cave opening. Unlike the previous cave, this one actually contains a back door to the caverns of the base. However, Sephiroth would have to be closely looking to the back of the cave to notice that it continues on and does have the secret exit.