What of the Nerevarine? Neither blight nor age can harm him, so in theory he'd still be around. Would he give enough of a shit to intervene in any way? Maybe some sort of resistance movement, that'd give you a nice war to beat events out of. Plenty of places to hide underground in Skyrim for a resistance. Maybe a reconciliation of the remaining imperial forces and the Stormcloaks to fight against this. The Aldmeri Dominion would take interest in another power trying to gain influence. You'd probably be looking at another Great War. With no Dovahkiin to stop him, Miraak would have returned to Solstheim, and he had plans to take over Skyrim. In fact, there's a fun further plot twist possibility, Miraak, with his mind controlling thu'um could easily usurp Alduin, or be using him as a puppet the entire time while aiming for ultimate control from the beginning. Dragons are naturally ambitiious creatures to begin with, any way you look at it, Alduin wouldn't be satisfied with only half of Skyrim. Also without the Dovahkiin, nobody would have stopped the prophecy from the Dawnguard storyline from being fulfilled, so your new world would likely be one of eternal night, allowing for vampires to take to the surface. All kinds of shit you can do.