The Siege of Szigetvár was very much a Pyrrhic victory for the Ottoman Empire. But it could have turned out even worse for them. Sokollu Mehmed Pasha, the empire's Grand Vizier, narrowly avoided being killed in a power magazine explosion.
What if the vizier had died in the blast?
Nikola Šubić Zrinski (Zrinyi Miklos) becomes even more a hero to Christendom ;-) with possibly minor changes to ethnic iconography in the late 19th and early 20th centuries (insofar as it either becomes a ‘glorious tragedy of Croat fighting Croat in the service of foreigners’ or used as a signifier in Croat-Serb wars’, depending on political context. Probably both)?
In relation to the immediate present, probably not much change. Both armies are disorganised or destroyed and can’t do much more. At other times Sultans or Viziers died without big changes. The greater impact would be in terms of Ottoman internal politics given the quick succession of death of the first two in the Empire - Sultan and Grand Vizier - who takes over in his place, the extent and duration of infighting, how it affects succession politics. I would think that, given Hurrem’s victory over Mahidevran - with the death of Mustafa - occurred a decade prior, Selim has no real opposition. Given it is the late 16th century, ottoman expansion slows further for a period but small-scale raiding continues in the borderlands of Hungary, Dalmatia and Croatia. It is unlikely to affect the Egyptian or Iranian/Caucasus fronts I would think, given the disparity seen at Chalderan only 30 years before.