Seems unlikely to plummet to ruinous levels. Ridership has risen by 800 million people since 1990, but there's fewer miles of track and only a few dozen cars. It seems that the system is strained well beyond its limits and that it might be possible that having fewer people use the subway might allow a chance to fix it? The issue seems to be largely administrative based on every article I've read. There needs to be an agreement by everyone on what how to move forward, and then for that plan to be implemented uninterrupted until its completion. But good luck with that since the mayor of NYC is basically a governor and the governors of NY always seem to butt heads with them.
It's not so much that the rail itself was destroyed, but that the tunnels and stations have been closed for various reasons. Usually it's down to either a new replacement station being built, consistent signal issues, or some other passenger safety concern. Of course there have been closures due to the maintenance gap, but those aren't the bulk.
