In Canada, we have a TFSA which I believe is somewhat similar to a Roth IRA. 

Firstly, if you sell the whole RVX company, there isn't a tax issue for RVX as Pharma would buy your shares directly from you. That isn't the scenario you were discussing so I will talk about a partial purchase for just Apabetalone. There are many ways to handle this. I will just lay out one scenario so that you realize that there are a variety of ways to do it that might not have been thought of. With a partial sale, RVX would need operating cash to continue to develop other molecules. 

RVX could create another legal entity and place Apabetalone and any other molecules that they wanted to include in the sale. At the same time you would still have your same share holding in RVX and their remaining IP. They could create new shares equal to 5 times the existing number of RVX shares in Newco. Of these, they could issue 4 of every 5 to the shareholders and retain 1 of each 5 owned by RVX. This happens sometimes with share buybacks that not all shares are cancelled right away. They might just be held by the company until they issue them to someone new (maybe in a PP). Using some very simple numbers, we could envision RVX owning 250mm Newco shares and the the shareholders owning 1 billion shares of Newco. If the sale was for $5 billion, it would be worth $4.00/share or $20/share of the current RVX shares. What you receive is before taxes as always and whatever situation you have will decide your net. You might have it in a Roth IRA, TFSA, RRSP, IRA or taxable account where it is capital gain. What you will receive is still $4 or $20 and I believe that was the term Cabel was using. In this example, Pharma would pay the shareholders $4 billion or $4/share for 1 billion shares of Newco. It would also pay RVX $1 billion for its 250 million shares of Newco. RVX would have operating cash to develop remaining IP. We would have received 80% of the value of the sale upfront and 20% would have stayed in the company within our RVX shares. Just one example!!