He is not dead
I don't think Wes is dead. I think the body is a look alike. Annalise would do anything to protect Wes; he is the one who killed Sam, he shot Annalise and he is now implicated in the death of his birth father (Wallace Mahoney). They made a big point this season in saying over and over that all they do is protect Wes.
I think instead of taking the blame himself, Frank found a body or killed someone and planted him in the house, then started the fire. Frank owes it to Annalise to again help her and he and Bonnie know how important Wes is to Annalise. I thought about Wes faking his own death too, but I think he loves Laurel too much to leave her. I think it's all part of a twisted plan by Annalise, Bonnie and Frank. I don't think Wes faked it and left town on his own....not without Laurel.