وَإِنْ يَسْتَغِيثُوا يُغَاثُوا بِمَاءٍ كَالْمُهْلِ
If they seek relief, they will be relieved with water like molten metal.
«In» often presents a condition whose realization remains open or uncertain. «Idha» frequently presents it as expected, assured or habitual. These are rhetorical tendencies whose application depends on context.
The verse frames a hypothetical appeal and a terrifying consequence. Its conditional syntax should not be mistaken for a promise of comforting relief.