They haven't stuck to that timeline at all.
> Classic Hangouts will be retired for all G Suite customers starting in October 2019
Chat within Gmail is still hangouts. Hangouts.google.com still works. Users still use the hangouts apps.
On the personal side, if you use Google Fi, SMS integration is still only available via Hangouts. This is a somewhat unique feature of Fi and Google Voice. You can send/receive SMS within Hangouts via browser or app all the same. It's not like the Messages app for web (which relies on your phone being online).
They have a newer timeline at https://support.google.com/a/answer/9197126?hl=en&ref_topic=...