Sigh, yet another example of hot shot teams using MongoDB just because it's new and sexy. Existing, established tools such as Oracle and Postgres would have offered lots of ways of avoiding such a problem.
I am a huge fan of postgres, but removing an index on postgres like this (especially if it is the primary means of querying a large table) would have the same effects.
This is just a failure of the tool that executes indexing operations, and not of the db itself
Although it's probably not directly relevant to this problem, I agree with you. MongoDB is the new MySQL; early on the scene and sexy, but at a real cost. There are other solutions doing the same things much better, and your life will be easier if you do your research before jumping into the sexy solution.
Companies should think carefully before introducing MongoDB (or any immature project) into critical production stacks.