I don't think that the notes operate in the way you are proposing. The notes are convertible at $14.63 per share. They cannot be converted at a lower price. They can put their notes (not shares) back to the company on the dates you outlined and receive cash. The cash they receive equals the face value of the notes, not some equity related value. Or they can hold the notes and hope for a higher price than their conversion price. If they put the notes back, they only receive the coupon interest payments (which were 2 5/8% I think). The reason the rate was so low was because they had the built in equity option. If they put the notes back to the company, those equity options built in to the bonds expire worthless and all of that value, the difference between the rate for notes without equity and rate for notes with equity (my guess would be around 7% or so) accrues to the benefit of ISIS and its shareholders.
Any buyer of ISIS would have to consider the impact of these notes, but only if the purchase price is above the conversion price ($14.63).