With all of Northern Zebrica under their spell, the three sirens are at the peak of their power and poised to invade Equestria. Obviously, now is the best time to follow Sonata's suggestion to hit the beach and leave the country to run itself.
"When the dust has cleared, and victory denied; a summit too lofty, river a little too wide. If we keep our pride, though paradise is lost, we will pay the price, but we will not count the cost."