It took me a few days to mentally process the fullness of what it means for Star Wars Galaxies to close its servers at the end of this year. Of the major MMOs I have played or have payed attention to, it is the first to completely shut down (and I believe one of the first major titles to shut its servers and not go to a F2P model).
While SWG should pass on, as it has too many bad memories for vets and has major competition coming out soon, it is a landmark moment that it is shutting down. MMORPGs are supposed to represent people in an alternate mode. People had houses, guilds, equipment, tools...things they quested for or built themselves. They had an alternate personality in that universe. With the servers shutting down, these alternate personalities are going to be permanently gone.
While Star Wars Galaxies has dropped in population drastically, it sets a president that is dangerous for MMORPGs in the future. Imagine, for example, if World of Warcraft announced a shut-down six months from now, where everything would be deleted, and the game would cease to exist. For WoW, there would be riots (if half of the angry nerd/kid videos that exist are legitimate). Sony Online Entertainment made the decision that it was not profitable enough to renew their license and maintain the servers. What is to prevent Blizzard from making this same decision? The answer is nothing. Most MMOs that are experiencing their Twilight years are going Free to Play, maintaining a reduced number of servers by a cash shop. Personally, I do not see Blizzard doing this, but I have a bleak view of the gaming giant.
In any case, this shut-down has implications beyond SWG, but as long as your favorite MMO has a large active population, you have little to worry about. The one concern I have is space giant Eve Online, that has been steadily dropping in population because of poor management and their last few major updates (including an addition of a cash shop with appearance altering items that are largely not visible by people other than the player). It should hold on for a few years still, but many of the major players are leaving and it will soon be more difficult to find people to perform difficult high-level jobs. Things like trusted third parties and statistical analysis of market data are starting to fall by the wayside, opening up people to more scams and other undesirable parts of Eve. I will be watching these events as they unfold.