I don't believe, however, that the use of an IM server within Zimbra is a viable option and unless there's a major shift in policy I guess it will be removed as stated in the bug report. What replaces it should be the discussion, surely? The bug report states in the first comment that there will be integration with external IM server and the (current) bug reports that cover that are:
Bug 19398 – Integration with external IM servers (XMPP proxy support)
Bug 42786 – Implement XMPP "Send File" in ZWC
Bug 45932 – Remove IM server
Perhaps those RFEs should receive the attention of this discussion and votes (if you haven't already).