The problem is, if everybody do what they want, then how could Bethesda continue making other games. If in Arena you would let Jagar Tharn live, then Dagerfall might not exist, and maybe no Morrorwind and so on. If you kill Alduin, in the next game this will apear in books and etc. If you don't, then they make a game in which Alduin returns. So, since they're not going to do a TES VI in which you can choose wheter Alduin is dead or not, that's a problem A good fix is to go back in time - in TES Online the events happen long before the main storyline in any game, so you will be able to have MAJOR choises. Also, I wish to note that Serana had, before imprisonement, about max 200 years of life. (Because she was imprisoned before the first empire and year 1000, First Era.) I just think this is another of Bethesda's Easter Egg and conspiracies.