One day on impulse...
To be able to assess whether the death at the end of the short story "The Red Convertible" by Louise Erdrich is suicide or accidental drowning, it's important to consider the background. The story concerns two Chippewa Indian brothers named Henry Junior and Lyman.
One day on impulse they buy a beautiful red Oldsmobile convertible together, and they begin to take it on road trips. On their longest trip, they take a hitchhiker all the way to Alaska and stay for a time with her family before returning home. Erdrich includes this interlude in the story to emphasize the intimacy and sense of fullness of life that the brothers share.
When they get back from this trip, Henry Junior is drafted to serve in the Vietnam War. He stays away for three years, and when he returns, he has changed. It is obvious that whatever horrifying experiences he went through in Vietnam have given him PTSD, or post-traumatic stress disorder, a psychological condition that afflicts people who have gone through terrifying events. He is no longer the relaxed, easy-going brother that Lyman knew in the past. Instead, he is tense, irritable, and always uneasy.
Lyman thinks that Henry Junior might improve if he works on the red convertible, and so he deliberately damages it so Henry can spend time fixing it up. This therapy seems to be effective at first. When the car is in working order again, the two brothers drive it to a river that has become swollen and is almost overflowing with spring snow melt. The brothers build a fire and talk, and then they fight. At one point Lyman shakes Henry and implores him to wake up, and in response Henry says, "I can't help it. It's no use." This sounds as if Henry is in despair and doubts if he can ever recover from what he has been through.
After the fight, the brothers drink beer and get along better. It seems as if Henry might be improving. He abruptly exclaims that he has to cool off and jumps into the river. There is no indication that this is anything other than a spontaneous act. Once he is in the deep, swift-flowing river surrounded by rubbish, he says, "My boots are filling." Erdrich writes:
He says this in a normal voice, like he just noticed and he doesn't know what to think of it. Then he's gone.
This seems to indicate that Henry has not jumped into the river with the intention of deliberately committing suicide. It seems that he genuinely thought that he only wanted to cool off. However, once he is in the fast-flowing current of the river, it is possible that he simply decides to give up and not fight the dangerous waters, and so he drowns. The answer to the question, then, lies somewhere in between the two alternatives. He doesn't deliberately commit suicide, but once he is out in the water, he ceases struggling and lets himself drown.