Ahhhh makes sense i guess...
I read that, so it's a risk of holding onto souls and doing a big level up for cheaper skills vs lots of little, but safe, upgrades?
One thing i havent read anywhere; what if you unplug your ethernet cable, obviously no-one can invade you, but how does it handle trying to revive then?
If you unplug your ethernet then your playing offline. You wont see message left by others, nor blood spills where others have died.
Every time you die you start back at the start of the lvl. When you are dead you are in soul form which has only 50 percent of you total HP apart from that its business as usual also you cant be invaded by black phantoms when dead.
You only get your body form back by killing a major demon, helping another person kill a major demon via online play, becoming a black phantom and killing another player online or by using a type of stone that are not very common.
When your alive, you can invite others into your game by touching there soul signs which are coloured blue.
There is always the risk of dieing that makes the choice of backing down and returning to the nexus a good choice if you dont want to lose alot of souls. I've learned this the hard way but thats what makes demon souls exciting, do you return cash in the souls for upgrades, stock and repairs which means doing the complete level again to get to a boss encounter or do you risk it all by fighting a unknown foe.
If you do die, you will drop all your souls in a bloodstain, should you be able to return to that same point and touch your blood stain you recover all the souls, if you die trying to get to that point well tough luck because they have gone
Just a quick link to the wiki , this has helped me loads.
Demon's Souls English Wiki: Figuring it out, one death at a time.