tl;dr:
There's nothing left. Join us in exile on Discord.[discord.gg]

novaburn just made a forum post[forums.relicnews.com] with all the details, but the critical last bit is this:

novaburn 님이 먼저 게시:

I understand that for many this comes as a shock; especially for the modding community that sprung up on RN around many of their fantastic games over the years. RN has a massive information resource for modding their classic games, and the fact that Gearbox utilized a lot of our information and tools developed right here to help them kick start the Homeworld Remastered Project is something we are massively proud of being a part of in whatever small fashion that is. For many others a final closure has been expected for long time. In the interim, the remainder of our community that was residing on our IRC channel, and then our Slack, and now finally our Discord channel can be found here:

"15th Fleet" - Discord for the remaining RN community where we talk nonsense, games and other related topics. Oriented more to a generic hangout and casual area for chatting. NOT relic/homeworld/CoH/DoW oriented at all.
https://discord.gg/0nD9jAgCPFSRmm5h


The Blackbird Interactive and Homeworld (DoK, Homeworld Classic/Remastered) specific Discord channel run by our good friend Tupper can be located here:
https://discord.gg/WGmRe2F

The wonderful folks over at Gearbox and their Homeworld forums are located here:
http://forums.gearboxsoftware.com/c/homeworld

The Relic forums for Dawn of War:
https://community.dawnofwar.com/

Company of Herores:
https://community.dawnofwar.com/