disconnect doesn't actually hang up the connection. If you have previously specified a reconnect for the connection, it will take effect immediately.
You can switch rapidly from session xx to disconnected session zz by typing
reconnect zz;disconnect
Then xx and zz will be reversed, and you can switch back and forth without trouble.
Normally disconnect disconnects the session specified by environment variable PTY. Given it will instead disconnect session ext.
Note that, unlike the previous version of disconnect, this version guarantees that the session will be disconnected before it exits, unless it fails with an error message.