With initial hype but failed promises, live service games have gotten a lack of trust from players due to poor performance. Therefore, is it worth investing?
If it's self-hostable, it absolutely is. I self-host Minecraft on my home LAN and my kids can absolutely play even if the Internet goes out. That's by definition offline, though you can certainly put it on a public server if you choose.
No, you can't. They decided not to give you that functionality. But amateurs are able to get pirate MMO servers up just fine until the lawyers come through, so it's all possible for us to do if they let us.