Unfortunately, it seems to be still a missing option as it is a double confirmation when deleting a checklist saying that it cannot be undone...
What I found that works for someone was:
If you have Trello on your phone, you can access the old list and type the items back on your computer. By turning off Wifi and Cellular (or placing it in flight mode), you can access the previous version of the list you used on Trello.
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