What happens generally with MMO's, years after release ? Does the server eventually shut down and render the game useless ??

In some cases, yes, but there are MMOs that have been going for a long time and are still running. It's economics really, how expensive is the game to run and maintain vs return on investment.

Ultima Online and Everquest are the oldest (and where the first, if you discount Meridian 59 which bears some contention) and are still going. Not strong perhaps, but they're still there - UO is still a subscription game, even, so that puts paid to the exclusive "subs are dead" argument.

That is simply, there will be some new games emerging, but the old king of MMO ESO will still have milions of players and we will be trolling and criticizing every new game untill some TES X is created that allows all wishes to become real.

Depends on the game's overall success. Yes it's reliant on servers so eventually, one day, it's doors will close. Could be two years, could be 15 or more - it really depends on whether it's still commercially viable for the publishers and developers