Both Dr M and LE will be multi-billionaires if they sell.

Leo will have pulled off one of the most successful business models in history by taking a 2 man company to a multi-billion dollar sale in a matter of a few years.  What does he have left to prove to the business world?  Does he want to have to go thru all the headaches of bringing these products to market and the haggling over licensing, accounting, etc?

Dr M is a lab rat who's only motivation IMO is to bring as many powerful, world changing molecules to the world as possible.  He cares nothing for having a company and all the headaches that entails.  I see him as far above worrying about material events and worried only about his work.

My money is on them selling.  It may not be the most lucrative option but how much is enough as they will still be EXTREMELY wealthy and have no headaches to worry about.

I agree with your thought that he could stay on to head development of the pipeline of products, though he would be some kind of independent researcher as he would never have to listen to anybody once he sells CTIX and a company would be a fool not to utilize his talents.  Again, win win for both sides.