Obvious answer is The Elder Scrolls franchise. We already have magic, orcs and undead so why not?
The MQ would be you looking for an old prophecy about your uncle.
You could heal your pre-war jet addiction by praying to the Nines. If you were too gud Dark Brotherhood and Talon Company would try to kill you, and then fight in epic sword fight who gets to kill you!
Nuka cola would give you frost resistance. Also dragons would blow up like cars. And radio stations would have bards.
And you could make BoS knights use Skyrim armours and swords and Imperial legions use power armour and guns! Epic!!
And everything would scale up with you, so at the beginning you fight with bandits in furs with pipe weapons, but later they get ebony power armour and daedric Fatman.
If you ever use this Emil, give me credit!