If Audi wouldn't have bought it, Lambo wouldn't have survived very long. The Kanto was in development, yes, but they didn't have enough money to push it further (their owners were hit hard by the asian financial crisis of the time). They would have been left with the Diablo, and sooner or later they would have gone bust. I don't know much about their awd system, to be honest (do you have any useful link for me? I'm always interested in learning more
), but as i already said, Lamborghini didn't have any financial support before Audi came. They couldn't have done it alone in my eyes.
To come back to the sales: yes, i know that Lambo has a maximal capacity which is rather small, but if you look at their sales, you will see that (even if it isn't their best selling model) the Murcielago is already a better seller than the Diablo. And from what i know, the brand continuously produces nore cars per year than before the Audi period.
Again, i don't want to defend Audi, but they really saved Lamborghini in 1998.