I don't think you miss out on experience if you die in combat (I still got the experience pop ups when I was dead while my friend was killing Orivand and his posse) but I really hate the fact that me and my friend's exp totals just leapfrog each others. I think I have mentioned this in another post about exp but if this is because of competitive questing I really don't agree with this. My friend and I are playing Co-operatively and want to be at the same level. Fair enough if one of us left the party to pursue our own agenda but even then I think competitive questing rewards should be purely materialistic (like gold and skill books, because you can still choose to divvy up the goods if you feel like it, giving you options).
Also I have noticed even in single player the experience is off. One example is when you escape the Fort Joy complex, your main character gets a CHUNK of exp (somewhere around 3.2k I think) and your companions get zip all. In this situation I couldn't help but think "This is single player, no multiplayer connection enabled, I keep all my party together so why have they got different totals"
