Personally I don't actually see the Ottomans holding Vienna for long, they don't have the option to starve the city out with the joint Polish-Austrian army approaching to take the Ottoman army out from the East. We know from experience that they lost the battle itself so their one big option is to assault the city which failed OTL. But let's assume for the sake of argument that Vienna falls, well it makes no difference to the ultimate outcome of the situation because their army will have taken heavy casualties from the assaults and the city walls defences would be weak.
The Ottomans might manage a slightly more favourable treaty and it might damage the Austrian reputation and their influence overall. But I'm not an authority in the subject at all so I can't say for sure.