without nyancat to control it, the rainbow becomes feral and, threatened by the rainbow road and mistaking it for an adversary, begins attacking it, causing both to collapse into photonegatives of their usual colours.
The heat from the explosion halts the ice age for 5 turns. The existing glaciers melt and form an ocean, where an injured Cthulthu retreats to take a nap. The ocean will refreeze once the ice age comes back, unless something else happens to prevent it.