The real question is: will I die if I ride an dished freewheel converted to single speed versus an undished wheel with a flip-flop hub?

Depends upon the quality of the wheel build and that goes for both wheels. Geared riders put in many millions of miles a year on dished wheels and very few die; even fewer due to rear wheel failure caused by the dished spokes.

An undished wheel is stronger but the dished wheel could be stronger than you'll ever need if done right.