I didn't love the ending either, but I see what they were trying to do. One struggle throughout the film is to understand who the main protagonist(s) are...I think perhaps the ending answers that in a subtle way. A decent film, but I'm surprised it's currently rated at 79%.

Ending was fine with me. It's clear Keller was found alive. He'd then be able to explain what Mrs. Jones had said to him, as well as what he did and why. It would align with what Loki saw of her before he shot her, as well as the drugged drink they'd find in her fridge. Whether he'd have had to stand trying for unlawful confinement is immaterial, another story (and I doubt any jury would fault him, given the gut-wrenching circumstances anyway).