They were kept as slaves. The Pharoah also started killing off newborn boys. They were actually too stubborn too leave. It was a migrant problem, the Egyptians were getting pissed because Israelite women were very fertile and they were starting to outnumber the Egyptians which is why the beef started up in the first place.
Yeah I've experienced the kind of miracles described in the Bible which is why I speak with so much audacity about this subject matter.