Would you recommend switching out Face of the Mountain for a Warmog's or something else when it comes to really late game? It sort of stands out there as an item that could definitely be replaced with something better.

well i guess your right, but with Alistar R you'll get a good amount of Armor and Magic resist wich will be like 50 sec or less, Rylais will do the AOE slow with your Q and will increase the amount healing of your E that's kinda the point since the patch increases suports abilitys with AP. but is a good sugestion ^^

I'd advise against the rylais. The 80 AP only adds 96 damage to your Q + W combo before late game resists (which they will have if you are on 6 items). Instead, I'd go randuins for armor and the AOE slow, which will be about as useful as the rylais slow in teamfights. Currently you have no armor in the build, but I think the randuins would fix that issue.