Well, every time I quit Armageddon and then came back, the first thing I did was start with an entirely new character so I wouldn't have to put up with all the stuff I'd have to deal with as a character who disappeared for couple of in-game years and then comes back with no explanation as to what he was doing during that time, even more so if it was a character bound to a clan of some sorts.
Besides, it gave me a chance to start anew and get re-acquainted with the world. I think that's where you should start, which also answers your question as to what you have missed. Find out yourself in-character, start again as if it was a different era in the same world. This allows you to get used to the mechanics of the game as well, all the commands and such while letting you get to know the new world.
As for whether or not you should return, well that very much depends. I myself had once successfully quit Armageddon with no intention of returning only to be roped back in further than ever by a friend of mine. Do I regret it? Eh, yes and no. On one hand I am completely addicted to this game more than I have ever been which means quitting won't be a thing I'll be able to do for a long time. On the other hand, the world that this game presents is vast and beautiful and most definitely worth investing your time in as I have.
So if you decide to return, I'd suggest playing in moderation. That means don't create a character that binds you to it in a way that it's expected for you to play it /very/ regularly.
If you do decide to come back, welcome back to Armageddon!