If it is a head injury it can take a long time for recovery...you may need to supplement and support him for many weeks... I know of many cases where they have recovered and equally ones who have not. It is impossible to say beforehand but if it was botulism (lethal dose) he would have died by now...if you have been giving him the vitE/selenium supplements this should protect from permanent damage in most cases once recovered... just be careful because the selenium is cumulative (meaning at a certain point you must reduce giving it to just a couple times a month and yet give a source of E weekly).
It is all dependent on yourself and how much time you can invest in this bird.