Continuity mistake: When the "Flag-Raisers" begin stripping down to go swimming, they show a few of the Marines already down to their boxers. They switch to a shot of Bradley and then back to the Marines and all have their pants on.
Continuity mistake: When the marines start marching inland, where the Japanese are not shooting, you see several clips of the row of soldiers walking inland, then a clip of their waiting comrades, and then a clip of the soldiers - still walking in the exact same place, without moving forward.
Continuity mistake: When Ira exits the stadium after the flag show to vomit, the alleyway in which he vomits is at first dark. In the next few shots, it is lit up and then once again dark.
Continuity mistake: When Ira is leaving Chicago on the train, the train starts moving while he's standing and saying goodbye the last time. In the next clip he's shown right next to the train door, but that would have moved further away.
Continuity mistake: The monument was dedicated in November 1954, but Rene Gagnon (and Ira Hayes for that matter) didn't look one day older during the ceremony than during the battle 10 years earlier.
Answer: The movie insinuates that he was killed horribly but doesn't provide many details. Books about Iwo Jima have quotes from witnesses about what happened to him and they all say that he was very brutally tortured, including having his eyes cut out and his genitals removed and stuffed in his mouth. The book "Flags of Our Fathers" contains the following quote, "A few days later someone yelled that they'd found him. They called me over because I was a corpsman. The Japanese had pulled him underground and tortured him. His fingernails... his tongue... It was terrible. I've tried hard to forget all this.