Given the milestones it would be reckless to US share if there were reasonable doubt of eventual drug approvals, given what you seem to argue is a less appealing profit profile for this drug combo. If the profit profile is not clearly appealing there is also less reason to US share.
It would seem the profit potential v cost would need to be much better than a close decision to accept sharing costs and risks. If ENTA chooses the sharing route I would initially think that management felt strongly about the profit potential.
As an aside, I'm tired of selling calls. Hoping some of my holdings gets called away in October to the benefit of the remainder.