Bill Shatner, Nichelle Nichols, George Takai and Walter Koenig are still around.
We haven't lost any of the main cast of TNG yet (thought Marina Sirtis' husband passed this weekend)....those are really going to hurt for me when they happen.
For me Star Trek was what we (as a species) can accomplish if we work together. It represented a hope for a better future. Now, with the actors passing away, it's like each passing takes some of that hope away.