> Alternately, maybe just flush the PTO experiment into the toilet of history, reinstitute sick leave and true vacation, and give people enough of each that they can absorb those life events that eventually happen to everyone.

This is what I propose, although you say it more eloquently. Rather than trying to carve out cases, why not offer x months of time off for every y unit of time? Those who want to spend that time with their kids can do that. Why should I remain chained to my desk because that's not what I want to do?