I've got a flight coming up in a few days from MSP to KOA (through LAX). The MSP to LAX segment was cancelled and Delta automatically rebooked me MSP to SAN on DL, SAN to SFO on AS, and SFO to KOA on UA. I was pretty surprised they rebooked me on other airlines! I've never had something like this happen before and having trouble finding definitive information online about the process. This is all on a single Delta ticket since they rebooked me on these flights. Does that mean they will check my baggage through to the final destination, even across non-partner airlines? Or am I going to have to pick it up, re-check and go through security in SAN and again in SFO? Also wondering if I'd have to pay each time to check it with the other airlines? I'm a platinum with Delta but have no status on Alaska or United.

Thanks for any insights!