What about pressing the PS button? all recent games pause during offline play when its pressed; you can sign out of PSN midplay and pause if it does.
Demon's Soul is an indirect offline game. Even though most of the time you play alone, there is co-op, versus and a ghost system that are all happening at the same time. I think I mentioned above that other players can jump into your gave and attack you at certain times (not all the time). Even outside of the co-op and versus stuff, you see other players ghosts as they are playing the game in real time; they can leave notes on the ground to read or you can just watch them in a battle and know there is danger up ahead.
then you deal with the consequences
the consequence in this case being that atlus doesn't get my money. games that won't let you pause or pause when you go into your inventory can fuck right off.
There isn't a real inventory system. It's not a loot game and you will rarely, if ever, need to stop and change equipment mid-mission. There isn't much item management either. Different buttons on the controller switches between herbs and stuff or what weapon you want to use. It's not like it's an omission and doesn't make sense in the game; most of it is actually well thought out. But if this stuff really bothers you, I dunno, then don't buy it. I'm just saying it shouldn't scare you away if you played any online game. That includes things like Monster Hunter.