MongoDB durability and consistency with j= true and w:majority
This is not how it works. With j:true and w: majority, w1 would only be acknowledged when the majority of nodes actually had reported to the primary that they have put the operation to the journal. Since the primary went down, this acknowledgement would never happen. So in this edge case, you would only have to do what you'd need to do what you always need to do if a failover happens before a write operation is persisted: redo it.

Let us expand the example a bit: let us assume that the write was successful, and then the nodes which already received the writes minus one go down. Now, an election takes place. The new primary is elected basically by each remaining node announcing the latest timestamp they have in the oplog. So, the node which received w1 would win (since the oplog is processed consecutively for each entry) and the remaining nodes would start to process the oplog from their latest position to the new primaries latest position - w1 will be replicated and hence it will be eventually consistent on all nodes.