Can you rejoin after a disconnect?
Yes, in most cases. Infinity Ward answered this in its AMA: if you lose connection, you should be able to rejoin the same server as long as it is still running.
What we do not know
Infinity Ward did not say what happens to your gear if you cannot get back in before the match ends. Treat it as lost until Activision says otherwise.
If it happens
- Relaunch and reconnect straight away. The longer you wait, the more likely the server has closed.
- If you keep dropping, use a wired connection, as Activision Support recommends, and check the server status page.
- Check the official MW4 Trello board for known issues. At go-live on 20 October its DMZ column had none.
See platform requirements for connection basics.