I think nvs flat out way overpaid for idix at least on the hcv side which was the driver of the deal. They were probably bidding against themselves like the New York Yankees tend to do.
The deal was over the top imo, huge payments to the private shareholders and huge bonus money to those private shareholders if the hcv drug work out (I don't recall if they get bonus money for the hbv drug). That deal was several years ago as well.
The only recent deal I know of which was more lucrative than vrtx/jnj was the Fibrogen/Astellas hif-1 alpha deal. And they were actually structured quite similarly. By retaining the US as Fibrogen did as well and getting US like terms for the rest of the world, I like the deal better than the idix deal. The key to maximizing the products downstream economics to VRTX was retaining the U.S.
nvs is sure to make a move into the protease field soon enough. Maybe they have internal programs or maybe they'll pull one in. After spending a $1B or more on hcv they won't cede the protease opportunity just because they passed or lost out on 950.