My rebooking onto KE was proactive in the DL did not insist that I fly into DTW six or eight hours late and deal with the rebooking there. They sent my directly to the KE gateway.

Being rebooked onto a carrier that isn't a partner would happen only as a last resort. DL will probably make you wait at least an extra day for flights before that happens. In my situation, there was no discussion of putting me onto AA/oneworld or UA/*A flights, even with an expensive ticket.