Not sure if any other druids have solo healed Garrosh yet but did it for our kill last night, just thought I'd add the video incase any other druids considering solo healing it were interested. https://www.youtube.com/watch?v=N7dCCiJyAgU
Although we only got 1 empowered whirling in p2, there were periods where we got 2 and thats totally fine to heal through aswell if your dps isnt quite high enough. AFKing terrace is great to reset mitigation CDs and regen most of your mana pool.