NaCl (saltwater) inhibits plant growth and reduces crop yield by reducing soil water potential and limiting water uptake. But salinity stress, on the other hand, as a result of the application of saltwater raises ABA (Abscisic acid) levels in the shoot, which promotes stomatal closure, which reduces water loss. So in summary, the most likely result of what happens when saltwater drops on top of stomata is the closing or closure of the stomata to reduce water loss.