If your domain expires and you renew it, as long as your _dmarc record is in your DNS, your DMARC validation will continue to function as it did before.

OnDMARC will continue to receive reports and provide visibility.

Depending on when you renewed your domain, if your DNS records got deleted for some reason, you can always find your suggested _dmarc record(s) in your Control Panel in OnDMARC.
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