Look here: http://www.nexusmods.com/oblivion/mods/24606/?tab=4&&navtag=http%3A%2F%2Fwww.nexusmods.com%2Foblivion%2Fajax%2Fcomments%2F%3Fmod_id%3D24606%26page%3D1%26sort%3DDESC%26pid%3D0%26thread_id%3D124792&pUp=1

So basically, to be sure no quest-related bodies (like Permanent Corpses http://www.uesp.net/wiki/Category_talk:Oblivion-Permanent_Corpses be removed from game before you can find them (thus breaking the quest), one should DISABLE the option Clean Actors in the INI. That's the first option in the ini.

I don't know how many quests can stopped, but it has been mentioned that this one can: http://www.uesp.net/wiki/Oblivion:The_Sword_of_the_Crusader