I believe the fundamental mission of Chabad shluchim is to have non-observant Jews do more mitzvos, whether it’s putting on tefillin or praying for Moshiach to come. In fact, whenever I see shluchim on patrol, they ask men about tefillin, women about lighting Shabbos candles. I don’t think they have ever mentioned Moshiach directly.
As for believing the 7th Lubavitcher Rebbe is Moshiach: Among the oldest Chabadniks, some do believe that, but among the younger, i.e., under 60, most accept that the Rebbe did die and therefore cannot be Moshiach. I think the younger Chabadniks are waiting for the Rebbe’s generation to go to the Next World before accepting an 8th rebbe. Caveat: these are my opinions based on conversations with many Chabadniks. None of the have said exactly what I just wrote.