Possibly a buyout. IDIX no longer has the scale to be a standalone drug-discovery company in the antiviral arena, so it would make sense for the company to be sold.
The founder and ex-CEO, JP Sommadossi, was never replaced; instead, the CFO simply moved into the corner office. This is exactly what happened at CEPH when the founder and CEO, Frank Baldino, died in Dec 2010; a few months later, the company was sold.