The drunk is dead. There's no great risk to the safety of the train from striking a human or small animal (larger creatures like bears and deer can be a problem). There are a number of very dangerous places to pass out drunk, and it feels like that's not really a problem for railways to solve.

At-grade ("Level") crossings should be closed (and thus grade separated). Where that's impractical there are numerous options for ensuring the crossing is not open to railway traffic until it is clear:

In some areas it can be practical to employ a person whose duties include verifying that this crossing is clear and then authorising its use. Because CCTV is cheap now we can fit cameras and lighting and have them do this remotely for a large portion of the network.

Or we can use radar to protect crossings. The barriers drop, and then radar is activated (the small hazard introduced by using radar is mitigated because the crossing is closed, nobody should be in the area being illuminated by the radar anyway), if somehow there is a large object on the crossing even though the barriers are down, this means something went wrong. The outward flow barriers re-open to potentially allow a trapped driver or animal to leave and the system tries again, if this doesn't help the crossing is considered failed and humans go to investigate, they will find your broken down semi-truck.

The freight car should preferably be harmlessly derailed by trap points. If this is impossible (and the layout cannot be rectified) the presence of the freight car should trip sensors, either axle counters or track circuits, and close the section to traffic. Again humans will likely have to come investigate how that occurred when it cannot be explained and won't go away.