When doing a node replacement when other nodes are down we see the down nodes marked as up for about 10 minutes. This means requests are routed to the dead nodes causing timeouts. It also means replacing a node when multiple nodes from a replica set is extremely difficult - the node usually tries to stream from a dead node and the replacement fails.
This isn't limited to host replacement. I did a simple test:
1. Create a 2 node cluster
2. Kill node 2
3. Start a 3rd node with a unique token (I used auto_bootstrap=false but I don't think this is significant)
The 3rd node lists node 2 (127.0.0.2) as up for almost 10 minutes:
I reproduced on 1.2.15 and 1.2.16.