However, it is unlikely that such a conflict would involve only those two parties and not grow to involve other states. Iran lacks state allies (except for Syria, of course, which is hardly a state now), but it does have a robust, transnational alliance with nonstate clients in Lebanon, Syria, Iraq, and Yemen. Groups such as Lebanese Hezbollah or Asaib Ahl al-Haq in Iraq would almost certainly support Iran in such a conflict, including by targeting Saudi nationals in their own countries, but they couldn’t attack Saudi territory militarily with any degree of effectiveness.
However, it is unlikely that such a conflict would involve only those two parties and not grow to involve other states.