Mik's Scrolling Battle Text is what you need to download

As useful as the build in spell alerts are, I still use PowerAuras for notifications like that.

Just set one up for when you are in combat/but do not have Inquisition up. I do the same on my warr for battle shout.

TellMeWhen is a fantastic add-on for telling you when buffs are missing, present, proc'ing, expiring, on cooldown, off cooldown, whatever you want.

It can "tell you when" Inquisition is down, but not if you don't have any/enough holy power (as determined by you), or factor in how much health the target has left if you want to try to gauge whether it's worth it.

Personally I use it to tell me when I charge into to battle with Crusader Aura on, among other things. :)

It's not as pretty as, e.g., Power Auras, but in my opinion it's a much better communicator.

Depends on what you mean by "text popup" -- if you just want a bit of text to float by when the spell falls off, something like Mik's scrolling battle text can work.

If you want something to pop-up on the screen when an important buff is not active, I suggest using PowerAuras. It can be a bit daunting to set up. Sooo many buttons and sliders to fiddle with. But they're importable and I usually just go borrow one from the wiki and modify it to do what I need.

i.e. On my mage (and shaman) I have a power-aura that lights up when my shield falls off.

I'm also going to vote for using power auras. It CAN be daunting to use when you first start because of all the options but, once you figure it out, it can be used for freaking anything that pops up in game. I used to use it on my Enh. Shaman to make sure lightning shield was up and to tell me when MW hit five stacks with a neato lightning bolt icon that showed up over my character's head.

Seriously, even if you have a completely stock UI. Power Auras is a great addon to learn and use.