This behavior has now been merged into mod_s2s in trunk and is therefore obsolete when used with trunk.
It can still be used with Prosody 0.12 to get this behavior.
This module closes s2s connections when mod_smacks reports that a connection has not received a timely acknowledgement as requested, indicating that the connection is broken or the remote server is not responding.
With the connection closed, the next stanza to be directed to that server will trigger Prosody to establish a new connection, instead of queueing it on the potentially broken connection.
This should prevent messages from being stuck in a queue for a potentially long time before being bounced back to the sender as delivery failure reports.
Normally the amount of time it takes for a broken connection to time out is determined by TCP.
If this is deemed sensible behavior then it will likely be merged into Prosody itself somewhere.
With the plugin installer in Prosody 0.12 you can use:
sudo prosodyctl install --server=https://modules.prosody.im/rocks/ mod_s2s_smacks_timeoutFor earlier versions see the documentation for installing 3rd party modules