So I read a rumor (sorry, no link) that indicated they're not going to kill Hangouts, but they are trying to simplify their offerings. Right now, they have a few different applications that are doing text messages (SMS), IM, voice calling, etc. Supposedly they're going to expand Hangouts and try to turn it into a unified business communications platform similar to Skype for Business. Then they're going to have a few consumer-grade apps, e.g. Google Voice plus a messenger app similar to Facebook's.
I have no idea if that's true, whether the rumor was created by someone with inside knowledge, or whether it's pure speculation. Years of tracking Apple products have lead me to be interested in but doubtful of all rumors.