The latter is clearly more valuable - because it returns the value of XL-184 back to Exelixis after BMY has already financed a good chunk of deveopment. They are likely no further back then they would have been had BMS not dropped the partnership, but they gain all of the value from the seemingly positive news from development.
In terms of the $8 stock price, assuming nothing adverse occurs, I can see the stock drifting back to that level for certain.
The take-out option is likely on the table. The recent XL184 results were likely a game-changer for any previous negotiations. If a deal is in the works, I'm guessing an early spring deal at US$15-17. If you look at the MEDX time frame - it was much longer, but BMY came in at a real low ball initial offer after underwhelming FDA feedback. I think Exelixis is in a stronger negotiating position and suspect there may be some interest in icing a deal more quickly, to offset any premium that would have to be paid with strong results at next year's ASCO meetings.
Best of luck everyone - it has been an exciting few weeks.