Hello and welcome to the forum @stephen7,
Sufficed to say there's already a topic on the forum about this subject here: Discovery UK are removing Discovery channel!
Has it finally been removed from Now TV?
Nope, the Discovery channel is still available on the NowTV service and i haven't heard of any plans for it to be removed since Sky / NowTV renewed the deal back in 2017
Thanks after an hour of the no longer available message, a reset and giving up and watching something else it has come back on