It's a big pity. Even though it's a walled garden, Google technologies have the advantage that at least most people have a Google account. To replace it, I have Whatsapp, Signal and Telegram running on my phone. I need all of those (and messages.android.com) running on my PC.

I guess Google couldn't figure out how to monetize it.

They have been slowly moving thing off hangouts, and I imagine they will just shutdown the IM part of hangouts to start with.

I thought Fi and GSuite already didn't get along ?

you can use hangout for Fi text messaging, but it's not required.

Yes. "Hangouts Classic" goes away for GSuite users Oct 2019, and they get migrated to "Hangouts Chat".

"Hangouts Classic" is going to be shut down at some unspecified date after that. All users will eventually be migrated to "Hangouts Chat" - GSuite users are just getting pushed first.