Create Checklist > Create Task > Decide to create a card from task > The task disappears.
My recommendation is to provide a secondary and tertiary question.
Question 1: Create a Card and Delete the task?
Question 1 Notes: If they choose this option then delete the task from the checklist
Question 2: Create a Card and keep the task?
Question 2 Notes: If they choose this option, ask to sync the card with their done column and mark the task in the checklist as done(This could be configured to work with the "Complete Card" option in the card. The workflow would also be able to be used as once the card is marked complete it would update that checkmark.
PLEASE VOTE ON THIS!! it aligns with the high voted card: "Show progress bar for parent cards"