LogFAQs > #979359687

Soloing works until you beat the base game (NPC groups can be used on all base dungeons and even the base game final boss). Then you will be forced to group up online for a "boss" fight post base game, pre-first expansion. Most, if not all dungeons through 90 that can be "soloed" using NPC groups. But sporadically the game will force you to group up to beat bosses. It will generally be 2-4 online bosses per expansion. The game also forces you to do three 24 man... or was it reduced to 12 man? Been awhile, don't remember... online level 50 raids (not one right after the other though) between the first 2 expansions. What happens is you cannot continue on with the main story quests until you beat said level 50 raids.