Is there anyway to recover the content of those boards?
If I upgrade again, will those boards reappear, or are they now lost. I can do the upgrade, but don't want to pay for it unless I can recover that content.
If those boards were closed then you can re-open them without upgrading to a paid plan. Since there is a 10-board limit in the free plan, you would have to close other boards to make place to re-open boards https://support.atlassian.com/trello/docs/reopening-a-closed-board/
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