Decision theory (which includes the study of risks of that sort)

No, it doesn't. Decision theory deals with abstract utility functions. It can talk about outcomes A, B, and C where A is preferred to B and B is preferred to C, but doesn't care whether A represents the status quo, B represents death, and C represents extreme suffering, or whether A represents gaining lots of wealth and status, B represents the status quo, and C represents death, so long as the ratios of utility differences are the same in each case. Decision theory has nothing to do with the study of s-risks.