The percentage of users that solely used the 3rd party apps to view and comment was relatively small.
Reddit doesnt produce any content itself, so viewing and commenting in general isn’t particularly important. What matters more are valuable contributions. I would posit that 3rd party app users provided disproportionately more valuable content than the official app users.
There is already an army of repost bots which aren’t going away. The bots don’t care about the health of the platform, so we can assume they are at maximum repost saturation.
And reposts still require new content generation to make reposts. You can’t repost the same stale content perpetually.
I don’t think reddit is going to just die. But it’s popularity and userbase can dwindle over time. Tumblr still exists, but it’s a shell of its former self.