The 6 year gap will minimize the maximum penalty available a little, but not much. Given his history and the fact that he has been imprisoned before, there's definately a good chance that he will be again. However, he was involved in an accident last time and I assume that this time he wasn't.
The problem he faces though, is that the previous accident is probably now going to come back and bite him on the you-know-what big time. The court is most likely going to be of the opinion, that he of all people should know the dangers of drink driving and since he's still doing it, he clearly hasn't learned his lesson. In that case, I would also expect them to take the view that the 6 year gap simply means that he hasn't been caught and I would expect imprisonment would be the result.
His best chance of minimize the damage would be to get a lawyer. When it comes to DUI, you're pretty much screwed if you self represent and have any history at all.
Here's a very extensive blog article specific to QLD. I recommend he read it:
https://www.harperfinch.com.au/blog/ultimate-guide-drink-driving-dui-laws-queensland/
