I have seen two solutions to this in other plugins.
A) The easy one but not so good.
Every unsuccessful order gets status canceled. So the user cannot retry to pay. He has to go all over again and fill the basket. Better than letting the user believe that he can retry and lead him to an error page.
B)Redirect to a confirmation page where it fixes referrer url and data to post.
Maybe in a latter version.
Cheers