@Paolo_Rovelli as @Danny said you can't undo deletion of a checklist, however you can see in the card's activity history when a checklist was added to a card, and you can also see which items were completed. This means that you can partially reconstruct a checklist by seeing what it was called and which items were completed, but not which items were incomplete (because there's no action history available for a card on checklist items having been added).
@Paolo_Rovelli Not sure, I'm not a member of the Atlassian or Trello teams :) I think at trello.com/contact there's an option to submit a feature request. It's something I've seen mentioned on here once or twice in the past year, but based on frequency I'd say that your request will be a long way down the list with many more obvious priorities. If you wanted to protect against this in future, you might consider implementing an automated backup of all your events using Google Apps Script, this is a good primer:
Hello Community! My name is Brittany Joiner and I am a Trello enthusiast and Atlassian Community Leader. I'll be sharing with you a series of videos with my top tips on how to best use Trello...
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