IHeart is an excellent and very user-friendly app, for what it is. And unlike Pandora, they have other features as well, such as access to live radio streams from select station groups. I typically recommend it over TuneIn for novice smartphone users who aren't outrageously picky about their selections, as TuneIn can be a bit intimidating, though a must-have for radio geeks.
There are many other players in streaming music nowadays. Slacker is the most like Pandora, and like Pandora is easy to use and set up. I've been getting into Songza lately, as their curated playlists cover pretty much any musical genre available. Plus, it features custom channel creation like the others.
I've tried quite a few others, such as Last.fm, which was too confusing. I uninstalled the mediocre Radio.com app from CBS once they re-added their streams to TuneIn. Not much into Spotify, as it's hard to control while driving. Google Play Music is crap.
But to answer the original question, no, Pandora won't wipe out IHeart or any other service. Everybody knows what Pandora is, as they've been around longer than any of the other custom-radio services. If anything, competition has grown, particularly in the smartphone era.