Following your question, here is a response that might help.
As per the board categorization in Trello(Free team board, Personal team board and Paid Business class).
Basing on the plan you are using the first two will simply be on the free plan with some limitations.
I thing the Business Plan Open as many team boards as your team likes, there are no limits. Therefore, in case of upgrade or update previous data will still be available.
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