They probably can. But then what? History is not over yet.
Egypt thinks of Ethiopia as enemy state. A lot of Ethiopians believe Egypt supports every rebel group in Ethiopia. But Ethiopians still don't view Egypt as an enemy, more like a thorn on the side. For thousands of years the Nile has been flowing toward Egypt without much objection. Bombing the dam will change that. It is the equivalent to creating a monster at your water source. Ethiopia will not try to block the water or anything like that. But it can and probably will start small irrigation projects everywhere. And it will stop consulting with Egypt. In the end, this will be much more devastating to Egypt than a hydro-electric dam which isn't even used for irrigation.
What baffles me about the Egyptian stance is, climate change is coming. Projections for fresh water in Africa in the coming decades don't look rosy. Mitigation for this is, fresh water sources should be developed and protected from environmental degradation. And you need the cooperation of upstream countries to do that. Being source of 85% of the Nile, Ethiopia's support is needed to do that.
Even if Ethiopia stops constructing the dam right now, in 50 years, at a time Egypt is sporting 200 million souls, there is potential that water levels on the Nile are probably going to decrease purely from climate change.
The talk of war is stupid. Playing zero sum game of "Only Egypt" is a bad idea.