Is it reasonably safe to visit Ethiopia and then to fly from Ethiopia back home via Cairo?
If you’re specifically interested in the Cairo leg then yes, it’s safe. Cairo is a modern city if over 20 million people. Tourism is Egypt’s most important industry and they are very, very good at protecting that cash cow even during times of political turmoil. If you pay attention to the news and don’t go actively looking for street riots to get involved with you’ll be fine.