The premise is fairly simple. Erich Ludendorff took some rather extreme risks capturing the Fortress of Liege. Imagine that he had been killed. I actually suspect this would have a minimal impact on the Western Front. It might slow down the capture of Liege by a day or two but ultimately I suspect this would have a relatively small impact. I would invite disagreement on this point.
The far larger impact, I would suggest would be in the East. In late August, of OTL, as the Russians began advancing far more quickly than anticipated Ludendorff was suddenly sent East and picked up the (recently retired) Paul Von Hindenburg on the train ride. They went on to command the armies that won the stunning battle of Tannenberg completely destroying one Russian Army and forcing another to retreat. Therefore, the question is would the Germans have won a similar victory with another pair of generals. If the Germans had not won such a stunning victory what impact would this have on the war.
The far larger impact, I would suggest would be in the East. In late August, of OTL, as the Russians began advancing far more quickly than anticipated Ludendorff was suddenly sent East and picked up the (recently retired) Paul Von Hindenburg on the train ride. They went on to command the armies that won the stunning battle of Tannenberg completely destroying one Russian Army and forcing another to retreat. Therefore, the question is would the Germans have won a similar victory with another pair of generals. If the Germans had not won such a stunning victory what impact would this have on the war.