I was wondering what would you think about switching from an MMO to a game such as Diablo. You have said that D3 plays similarly to D2, yet the latter came out many years ago, when the community had not reached the stage of persistent world population, and the social ties that you could form were not as strong as in MMOs. Many people are migrating from WoW and other MMOs into D3 - would they like this step backwards into lobby-like gaming?
Could you play without a persistent world, without a community?There are multiple ways of looking at this question.
First, for me at least, Diablo is closer to a single-player game than a multiplayer game. Multiplayer is fun, but the first time I play any level, it will be as a single-player. You can go at your own pace, listen to all the voice-overs, experiment with different abilities, and ensure that every single barrel on the level has been broken before moving on. I suspect that the initial play-through for the majority of people will be similar, or maybe co-op with a real-life friend.
In this view, community really doesn't mean anything for a single-player game.
Second, if you play an MMO in a transient fashion, you will find that it is very similar to lobby-like gaming. You have to join the community in order to experience that sense of community. And a lot of people don't join the community. I know that I have never done so in any MMO other than WoW.
So D3 would be just as persistent as my experiences in RIFT, Age of Conan, Lord of the Rings Online, etc. Of course, that may be the reason I never played for more than a few months.
However, I really think that the MMO literati gravely underestimate how many people actually play in this fashion, how many people are not part of the community. In my opinion, what we think of the community in many of these games is actually a minority of the total playerbase.
Third, even transient games have an external community consisting of the forums and websites, where people can discuss the game, brag about stuff they done, and commiserate with others who have lost high-level hardcore characters. I suspect that the people who do end up playing Diablo for years tap into this community.
Fourth, the final view I can think of is that maybe Diablo becomes the equivalent of television for a lot of people. Log in, kill some monsters, get some loot, and log out. Maybe zerg a boss with some random people online. Mindless relaxation to unwind after work. In this view, community is really not important, and may even be detrimental as you don't really want to spend brain power and effort on that community.
Personally I don't think I could play Diablo for as long as I played WoW without the persistent world and community. But I also don't expect to play it for that long. It's a single-player game for me, with a little bit of random multiplayer after. I will probably play Diablo until the next interesting game comes along.
 Technically, I did join a guild in SWTOR. If I had made to the cap and started doing things with them, I might have become part of that community.