The Prosecutors most likely cannot because, as noted above, the death before sentencing probably voided the conviction. Without a conviction there is no way for the government to impose a lien for restitution.
However, as noted in the above article, claims filed by shareholders against Lay and other senior Enron executives in a civil case can still proceed to trial. The question will be whether or not, by the time the trial is concluded, there is an estate left upon which to lay claim.
