I don't know how common this is, unused vars, but probably, yeah. We players never see them, after all. There are some vars in mods that never get used(in BG1 NPC, for one), too - some plotlines get abandoned and so on. Some of it gets resolved in BG1 UB - unfinished business.
Yep, setting deathvar to a vanilla game cre might get you into trouble. Check out the list of tutu mods at modlist.pocketplane.net and at forums.gibbrings3.net(general discussion - a pinned topic) - you'll be amazed. Beregost in particular is very popular. If it's at all possible, I'd recommend you to add your own new character. If you got your characters set in mind, see if it doesn't interfere with anything. jastey's mini quests come to mind, or Gavin, or even BG1 NPC and BG1 UB. Also, please, make sure you get a modding prefix, you'll likely need one if you haven't already. Check forums.blackwyrmlair.net, first or second subforum from the top.