If the development occurs that proves to use rail in sufficient numbers, they can always scale service back up.  That's easy.

5 months of only 41 riders per hour is certainly long enough to see it's GROSSLY underperforming and warrants cutbacks in wasted operational expense.  But I am a bit surprised they're talking about going straight from every-15 minute service to no off-peak service at all.  I'd have expected something more like dropping to hourly service for 6 months first, and seeing how that does.

Of course, another consideration would be raising fares to try and recover enough fare-revenue to meet the 30% self-sufficiency requirement.  As I said, the R-line was always going to suffer from poor ridership IMO because it doesn't have the built-in incentive of saving people from high parking costs, like rides to downtown and DIA do.