Many ultra running events do meet roads where checkpoints/aid stations can be placed (or tracks that can be accessed with permission). In long unsupported stretches competitors might be a little better equipped than in the recent case (for example consider the amount of water runners carry on the Marathon des Sables) .
Of course if the bad weather brings poor visibility, runners can lose the route (even if well marked), and checkpoints are of limited help then. Note that the Gansu incident happened between two checkpoints that weren't far apart in distance, but on a section involving a climb out of a river valley, so slow and increasing in exposure. While poor visibility isn't mentioned in the reports I've read, rain and strong winds are likely to make navigation harder even below the cloud base.
The risks are arguably more about the terrain and remoteness than the length of race, though clearly a short race starting in a town can't get far from the town. Taking that into account, we might consider the fell-running (essentially hilly cross-country) community's approach, as they run in all sorts of weather conditions and usually without easy rescue/escape routes. This document from 1981 (UK) shows that the risks have been known for some time, and mentions several mitigations, requiring a certain minimal level of kit/supplies to be carried for protection from the elements and energy, and emphasising that the required minimum may not be sufficient in all cases.
It also discusses the need to respond to severe weather; responses may include cancellation, route changes (shorter and/or less exposed), or merely advising the runners. Clearly this is an old document, and written in a slightly different context, but the approaches are very similar to those used in other remote events: Require some level of self-sufficiency for emergencies from the competitors and keep track of where they are. The last point is where the biggest changes have happened. Trackers like Spot are often required and to avoid cheating, in running and cycling events. While they don't update all that frequently on long events a location is a great aid to rescuers and many devices have a panic button. More modern discussions of the risk (RunUltra), aimed at the runners rather than the organisers, recommend trackers for extreme events.
Update: Around the time I wrote this answer, The Guardian published an article including some interviews. Key points:
Some observers have questioned the lack of mandatory cold-weather gear other than an emergency blanket in the race’s equipment list, particularly for such a remote, high-altitude event. China News Weekly also quoted local rescue personnel saying they had struggled to locate people in the inaccessible terrain
On social media, Luo Jing, a well-known Chinese athlete and mountaineer, warned others to take their own safety seriously, suggesting the high death count was at least partly attributed to inadequate preparation for the surprise extreme weather...She said her life was saved by having warm clothing with her, and having enough time to descend.
and that the only mandatory kit in case of extreme weather - foil blankets - didn't hold up to the string winds
In summary: As in so many outdoor activities a big risk comes from worse-than-expected conditions; in that case improved modern forecasts help but the old rules of calling off/postponing the event, or having a more suitable route are just as applicable as ever. It's essential to carry some safety gear, but this has to be mandatory.