diablo-3
I'm not that big on knowledge of Diablo, but how in the hell did the 5 first evils got into the black soulstone?
And since we are on the topic, after that the 7 devils were trapped into it, Leah had to user her magic 24/7 to keep them in there… so how didn't the soulstone blow up during the entire years it was without surveillance in Kulle's lair?
In terms of your inventory and such, there is no such thing as the game "saving", updates are instantly applied to the server, so it isn't possible to lose anything. In terms of quests, there are frequent "checkpoints" throughout the game (usually about every 5-10 minutes). Anytime you stop playing, you will resume the quest from your last checkpoint the next time you start again. There is no way to force a quest save other than reaching one of these points.
Best Answer
You are told this in-game upon collecting the black soulstone (Source):
The other classes only differ in what they say when they discover it.