Final answer:
The provided excerpts do not include a direct answer to the percentage of Russell's climbing mates who have died climbing. Additional context or a specific source referring to Russell's statement is needed to provide an accurate answer.
Step-by-step explanation:
The information provided does not contain a direct answer about the percentage of Russell's climbing mates who have died while climbing.
To answer this question accurately, it would be necessary to refer to a specific text or statement by someone named Russell regarding his personal experiences or statistics related to the mortality rate of his climbing companions.
The passages extracted mainly deal with the challenges and conditions faced by climbers, a fictional account of Venters' climb, and a student poem about sleeping during class, but none of these passages provide the statistical information needed to answer the question about Russell's climbing mates.
Without the specific text where Russell discusses the percentage of his climbing companions who have died, it's not possible to give an accurate figure.
The topic seems to be related to mountaineering and its dangers, but the excerpts given do not lead to a factual conclusion on the mortality rate that Russell might have indicated.