It looks like Xumo Play (free app) has been acquiring more LiveTV channels, and ABC News is currently available on it. (not sure if it was there previously or not).
https://channelstore.roku.com/search/xumo
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Need to keep in mind that it may have been ABC News decision to remove itself from Roku Channel Live TV. Browsing the ABC website, seems to push Hulu and cable providers quite a bit. They only mentioned being able to stream ABC News Live on either their website or their app. They didn't even mention Xumo Play, so who knows where else it may be available. Can always cast from their website or the app to your Roku or TV.
https://abc.com/watch-live/abc-news and https://support.abc.com/hc/en-us/articles/360025228631-Where-is-the-live-stream-available-
With any of the free content available (be it on-demand or Live TV), users should be prepared that it will come and go. No amount of demands or foot stomping will change this fact. In addition, sometimes these channels will mysteriously reappear after a short absence (a few days to a week) so checking back is sometimes a good idea.
With Streaming, users need to remain adaptive and flexible to watch their desired content on different channels/apps if it becomes unavailable on their preferred channel/app.