I had a well-loved budgie who suffered a similar fate. He took off when a bird on a TV programme gave a distress call, and walloped into the livng room wall. He spent about a week apparently paralysed, couldn't mve or feed himself and only able to look out of one eye. But he didn't die. In the end I opted for euthansia and still feel very sad about the whole thing even though it was a long time ago.
The point is, you do the very best you can, and in the wild these creatures would die horrible deaths being chewed by scavengers. Even their own kind reject them when they fall ill. So in the great scheme we have done a good turn for a another being to the best of our knowledge and abilities. Don't beat yourself up about it. Hindsight is the most accurate science and we can all spot what we should have done afterwards. Concentrate on the truth that you did your best with the best of intentions, and then move on.