MongoDB replica index filled hard drive stuck in fatal
If your data exist on a node then this node is named Primary from now on and the other 2 secondaries.

1) Start the Primary as standalone and drop the index.

2) Take a backup of your data just in case

3) Stop secondaries and delete their data directory.

4) Start the Primary as a member of the replica set.

5) Start the first secondary. This will cause an initial sync of the data, when the member join the set as secondary start the other secondary.