to fully monetize the asset you would have to make the difficult assumption (closer to wild guess if you asked me) on probability of another generic entrant entering the market over a specified period of time. if NVS and MNTA don't see eye to eye on these probabilities, the cleanest way to monetize some of the asset is to sell 5% of the profit share and then reduce the royalty by a comparable or slightly greater amount (sales would be lower with another generic, but 5% of net sales is > 5% of profit so i don't think it would be much more than a 5% adjustment to royalty). this way that 5% can be valued as an ongoing stream in perpetuity and the proper multiple applied.
imo 5% should sell for 300M (300M earnings with no risk generic equates to value of asset of about 3B and they would be selling 5% of the 45% profit share or 1/9th of the asset)
if you take whatever up front money they get from a deal for M118, add 300M to the pie, that should cover their portion of development of the product and then some