[kenorian]

Several times now, my Google Now Toolbar goes away and an "X" is in it's place. Saying OK Google still works.

Rebooting the device clears it.

I'm using Nova Launcher, unsure if that makes a difference.

[B. Diddy]

Sounds like a Nova glitch. When that X appears, is it at the top of the screen? Does it look like when you long-press an icon and get the option to remove it from the homescreen?

The next time it happens, try going to the App Manager, selecting Nova, and Clear Cache.