If it's made by Blizzard, people will buy it.
Okay, something new was released today. Keep in mind this is based on first characters that aren't fed gear and gold by your main characters and only applies to few difficulties (probably Normal, Nightmare and maybe Hell. Inferno is on a whole different scale).
In my experience recently, if you're in a party of two or three, by the end of normal difficulty, if one person strays from the group and a pack of champions comes along, it's fatal.
I'm guessing that it's a little less risky in a group of four, but even then, probably only for a few more levels.
I'm talking about first characters, of course. Characters that are being fed gear and gold by higher-level characters can probably get by without everyone sticking together for a bit farther into the game.
My current motto for group play in Diablo III is "divide and be conquered".
He means that if 1 person leaves group of 3, the 2 people left grouped together will still die if they encounter hard mobs. The single person doesn't stand a chance.If there's a group of 4 and 1 person leaves, the group of 3 still has a chance to survive.
This.
And again, we're talking about two things that vary a lot: the speed at which your specific party can deal with regular enemies, and the degree of uptick in difficulty when you go from regular enemies to champions. The variance is on the skill of the players, and the affixes on the enemies. I'd guess that in some cases, a group of three players (in a game of four, where the fourth is away) are going to get along just fine for pack after pack after pack, albeit much slower than if their comrade was with them. And in other cases, those three players are going to rapidly die to the first pack they encounter.
Why? The answer will be their gear, or their mix of chosen skills, or the fact that the game happened to roll a pack of champs with lightning creeping all over the area, etc. etc.