I thought I'd add my experience for a trip that was to start Monday.
November, 2019: booked flight through Delta, as a Skymiles member (no special status). Depart MSP 04-May, connect/transfer at AMS 05-May, KLM operated flight to LIS. Return 16-May, AMS to MSP
November, 2019: booked separate hop from OPO to AMS through KLM, as a Flying Blue member. (Did not want a 5:00 AM flight from OPO to AMS returning to MSP.)
16-April: my hop from OPO to AMS was canceled, notified by email from KLM. Voucher only.
18-April: my 4-hour layover on 05-May for the LIS segment was reduced to 45 minutes, when reviewing My Trips on Delta.com.
29-April: trip no longer appears in My Trips, and a search for the original itinerary turns up no such route found.
Like most everyone else, I'm now playing the waiting game with Delta and will see what happens between now and the 4th.
Update: One of my siblings somehow received my trip cancellation email from Delta on the evening of 30-April. Our email addresses aren't even remotely similar; we are both Delta customers. The email is suggesting I redeem my ecredit. They canceled, and I will be requesting a refund.
This was to be have been my second European trip. I'll hopefully look forward to planning that second trip, for Fall 2021 or later.
Update 2: 02-May. I called Delta this morning. The entire process from start to refund confirmation emails took under 30 minutes (including a 20 minute callback wait), and we verified my email address, which of course they already have. No complaints, everything went smoothly, and I should get refund back to my cc at about 30 days out.
Also, I have my voucher from KLM, valid for 1 year from date of issue.
Best of luck to everyone else having to sort things out. Thanks to those on this forum who, in some form or another, provided intelligent and straightforward guidance (without all the drama).