IF NVS really thought IDIX were worthless, it presumably could've worked out a partial or full sale of its stake to Baupost or another institutional holder. Maybe NVS is holding for the possibility of an IP royalty on Sovaldi.
This topic has somewhat more than academic interest for ENTA shareholders insofar as NVS is developing ENTA's EDP-239.
“The efficient-market hypothesis may be the foremost piece of B.S. ever promulgated in any area of human knowledge!”