I am a bit confused by your question. If you are writing a topic sentence to take a position in regard to Gene's achieving redemption, you could choose to argue either way. However, there is strong evidence that Gene does finally find redemption, a separate peace of his own. If you chose that position, your topic sentence could be something like this:
After much suffering, Gene returns to Devon after fifteen years to relive his betrayal of Finny; having achieved a greater understanding of himself since leaving school, Gene is finally able to forgive himself and find peace.
If you are looking for a sentence from the novel that states whether or not Gene finds redemption, you won't find one that makes that specific statement. However, this sentence that appears at the conclusion of the introduction does suggest that Gene finds peace after returning to Devon after fifteen years:
Changed, I headed back through the mud. I was drenched; anybody could see it was time to come in out of the rain.
The most important word in the quotation is "Changed," suggesting that Gene's return to Devon had affected him in a profound way. The reference to its being "time to come in out of the rain" suggests figuratively that it is time for Gene to let go of the painful past.