For one, I get the feeling that this film will totally ruin Han’s arc in ANH. He goes from “cynical smuggler who cares only about himself” to “rogue who sacrifices his own interests to save his friends” in the course of the film. That’s his character. If they try and make Han out to be a good guy in the standalone movie (which they will; this is Disney we’re talking about here) it will spoil his character progression. This will make his whole subplot in ANH completely pointless.
The Special Edition of Star Wars already ruined his character. But yes, this could be the final blow.