The bases closest to Iran may well get overrun. Iraq and Yemen will fully enter the war. Bahrain will erupt. It is not unimaginable for the Houthis to capture Asir and Jizan (historical Yemeni lands) and Iraqis to link up with the Shias of Eastern Arabia which incidentally sit atop most of Saudi oil reserves.
They are going for broke. If a land invasion fails, geopolitics of the region and the world will change and in a fundamental, civilization altering way. It seems they will try regardless of the hazards.