WiredTiger is not with 2.4 version, it works from 3.0 verison. Make sure all mongos, mongo configservers and shards are of same version. Steps to recover is: Backup mongodump all the data on all 3 shards. Drop the databases on all 3 shards.(Instead can start mongo with new datadir, So you dont have to drop database, you still have data safe ) Add the 3 shards to the cluster now(there should be no error as its empty). Then Restore the mongodump's taken from 3 shards one by one. This will recover all your data. NOTE: You can test this in some staging setup with less data and verify steps.

We might need to backup the database on each shard. empty(drop) the database and restore one by one from mongos to the cluster after adding the 3 shards. What is the database size on each shard?. how may databases? verison? engine?.

@ahmedash95 are shards connected to mongos...and not able to see the database OR just no shards connected to cluster and no database is available.?

My understanding is, 1. you lost(disconnected) one shard which has 30G data from cluster. Later you got the other two shards also disconnected from cluster. Now all you need is to add those 3 shards to the cluster. As you cant see any shards from mongos. Please correct me if i got it wrong.