Egypt doesn't have the capability. Their air force has too little range and too little refueling capability.
IMHO, most likely result of an attack (for Egypt) is that Egypt loses a part of its airforce in return for temporarily harming Ethiopia's ability to generate electricity at the site. At which point Ethiopia fills the dam anyway and works on repairing the damage, while Egypt wouldn't be able to repeat this.
But yes, the planes would be expendable. That said, Egypt could very well breach the dam itself. It would needs some creative use of munitions but modern munitions are precise enough to allow for breaching of dams.