Blizzard story team: "Of course you can.
Of course, it’s a prerequisite to the story, so it won’t advance while you do so, and not completing the storyline prevents you from moving on to other zones, unlocking certain dungeons and raids, locks you out of Expansion-MacGuffin XP and locks you out of reputations needed for Shadowlands Pathfinder: Part One.
But sure, you can leave her there if you choose to."