After March 6, 2012 Malone-Liberty can do whatever they want with regards to purchases of Sirius XM. Plus, the Sirius XM shareholder rights plan also expires (another key) opening Sirius XM up to a possible takeover by just about anybody. However, with Liberty already holding 40% I doubt anyone else will make an attempt.
It might be that Liberty's stake in Sirius will split-off into a new company (WRSPQ) after August 1, 2011 and a merger of Sirius XM into that company. It makes the most sense on all sides, while allowing Liberty to do just about whatever they wish without any taxable event. (another key incentive to not rush)
Adjö