Zero percent change of happening: you cannot pardon someone who was not adjudicated guilty of a crime (by conviction or by a guilty plea).
Aaron died before his case was finally adjudicated (i.e, until all appeals were exhausted), so like the Enron guy, in the eyes of the law, he is not and never can be guilty of the crimes he was charged with.
Again, for emphasis: you cannot pardon someone without a conviction.
That's not what the Constitution says. The presidential pardon power isn't limited by this situation. The President is the only one who can decide who get's pardoned and under what circumstances (except for cases of impeachment).
From the source:
[the President] shall have power to grant reprieves and pardons for offenses against the United States, except in cases of impeachment.
"Acceptance, as well as delivery, of a pardon is essential to its validity; if rejected by the person to whom it is tendered, the court has no power to force it on him. [...]
There are substantial differences between legislative immunity and a pardon; the latter carries an imputation of guilt and acceptance of a confession of it [...].
The facts, which involve the effect of a pardon of the President of the United States tendered to one who has not been convicted of a crime nor admitted the commission thereof, and also the necessity of acceptance of a pardon in order to make it effective are stated in the opinion."
- Burduck v. United States, 236 US 79 (1915), Supreme Court of the United States, internal citations and quotes omitted.
Nixon was pardoned against future charges. The dead can have no future criminal charges. A pardon would be the same as the government just issuing a formal apology.
Right - the government shouldn't "pardon" him, they should apologize for the manner in which they prosecuted him. (I'm not sure they should apologize for prosecuting him at all, though.)
Aaron died before his case was finally adjudicated (i.e, until all appeals were exhausted), so like the Enron guy, in the eyes of the law, he is not and never can be guilty of the crimes he was charged with.
Again, for emphasis: you cannot pardon someone without a conviction.