Try exiting both Steam and Civ 5 then restarting. If that doesn't work checkout this link.

http://forums.civfanatics.com/showthread.php?t=465972

or post #3 in this thread:

http://forums.civfanatics.com/showthread.php?t=489135&highlight=disappearing+mods

i subscribed and selected it but i don't see any changes to the advanced set up

nothing:-(

For people who have problems with nothing showing up: You are probably backing out of the mod and not using it. When you reach the screen that says "Mods" at the top click on "Single Player" then on the next screen click on "Set Up Game" then on the next screen click on "Advanced Setup". Do NOT click on "Back" unless you actually want to back out of the mod.

Loving this mod!

I turned sicence off and now it wont turn it back on

I love this mod

I only want to express my appreciation for this brilliant mod!

this is a great mod, definitely up there as one of the few "must have" mods if you play the game a lot

best mod, it's a must have

Having similar issue, except I can't even activate it, much less find it in game. I opened up a seperate discussion for it.