Putting a marker in the ground of 1 July 2019 for first...

Putting a marker in the ground of 1 July 2019 for first commercial sale puts Rice on strong ground.  Note that whether there has been effective achievement of commercialisation is at Rice's determination.  That must have been the company's (and its lawyers') interpretation based on how they summarised the termination right in the Key Risk section.

I'd be concerned if one of the potential partners that wbt is talking to saw value in the tech and decided to negotiate directly with Rice for the IP

Rice would be obliged to consider any such approach and Professor Tour (given his conflict of interest as a shareholder of wbt) would be excluded from the discussions/negotiations. (I note that Rice Uni has a comprehensive conflict of interest policy.)

One of these parties could offer to buy the IP for cash, and then negotiate a new (onerous) licence agreement with wbt - or alternatively cherry pick some wbt staff and develop the tech itself.  

While this scenario may be unlikely, it would be catastrophic for wbt shareholders and hence it is in wbt's interest to negotiate some form of extension/waiver with Rice to remove the uncertainty.  This would likely have a cost attached to it ($$ for a another research project, shares, increase in royalty?)