Well, what this implies is very simple: necromancer is not making a come back!
indeed. his skills are very similar to the Witch Doctor skills we know about and as Blizzard said: No class will be similar to another. Necromancers are lore for now. So are corpse using abilities i guess.
Remember what Blizzard said? This game is specifically made for online playing, but single player option is available. So they'll obviously focus on multiple player gameplay.
If you can have the option to choose when the corpse disappear, that should only be on singleplayer, but this would not work on multi player (assuming most of you play online instead of single player.). If we assume the corpse could be used for something, maybe corpse explosion, wouldn't really make sense to have the floor randomly blow up if someone turned the corpse vanish on and some turned it off.
As someone have mentioned before, they should make the corpse vanish if the section of the area is demonless. So they basically split up monsters into groups, and split them in different sections of the area. And they wouldn't leave the section they were placed onto. When that specific section is demonless, the corpse vanish. But if their were say 1 or 2 demons left, the corpse don't vanish. This is just in case the demons can ressurect the other dead demons.
This way, they can control the amount of demons on screen each time, and avoid lag. Of course the corpse only vanish if the area is demonless for about 3-4 minutes.
I used to be crazy about Multiplayer, if the game wasn't about Multiplayer, I wouldn't buy it. Now that's changed, and I enjoy Single Player games more than Multiplayer now. Sometimes the online community is just garbage. I really hope they don't focus Diablo 3 to be online, I really don't. On Titan Quest / Titan Quest: Immortal Throne, I'd mainly do single player due to the fact I could go at my own pace, enjoy killing all the creatures without some player rushing to them all, and not have any players complete quests I haven't completed yet which if they did automatically made the quest completed on my side.
I'd then go on multiplayer casually just to showcase my gear, or mess around. Since Diablo 3 will " hopefully " offer some decent PvP, that's a reason why I'd go online mostly. The PvP brings the community online, so I hope Blizzard realizes that and makes it one of the key focuses instead of wiping it to the side like most companies do with their Hack N Slash game. But it sounds like Blizzard is incorporating the same Online system Titan Quest used in terms of hosting a server, and players being able to join at any time and pick up where they left off in their single player campaign. I also liked to go online for the increased difficulty, since every player that joined, popped up a message saying the difficulty has been adjusted, which added more creatures, hero level creatures, and loot.