Our [first world] leading causes of death are heart disease and cancer by far (totally outclasses anything else---if you can avoid those two, you will live a long life ... and then probably die of them in your late 80s or 90s) followed by things like accidents(*), strokes, Alzheimers, and tobacco (COPD). If antibiotics wear out, infectious diseases are going to go way up, but keep in mind that sanitation standards are way higher than they used to be. Another factor is drug abuse which becomes a factor if living begins to suck too much. In the US we have a growing opioid crises where people overdose on their painkillers. In Russia people drink themselves to death so effectively that their population was speedily declining in the 1990s. I think that will become more prevalent once growth stagnates and fades. Once people give up hope then drink or drugs begin to look pretty good.
(*) This is pretty much the only thing that can really kill a person under 40 these days.
I don't really follow the diversification gambit. Also what do you mean by one generation is not enough to diversify? What are you diversifying?
If we look at one generation at a time then when it comes to risk-adjusted ROI, one computer engineer > one amazon order picker + one busboy + one Uber driver + one paralegal + one hairdresser. Sure, the latter will always have some income combined, but the CE income will be higher than the rest of them combined and the CE will likely not be struggling for employment, spending 20+ years paying off loans, or working clopenings in two part-time jobs. Check out some of the higher spending journals here and see how much $$$$ they're pouring into their few children to give them an advantage over the other kids. That's K-selection and that's what the r-selection strategy is up against. That CE will in turn have another CE Jr. ... and so on. This is essentially how social mobility dies and the [socioeconomic] class system propagates. This effect is getting stronger in the US. The American Dream is dying here. If Americans want their children to live the American Dream, they need to go to Denmark
PS: I'm certainly biased in terms of quality over quantity when it comes to life/living. Maybe I'm just talking my book