I'd take a full backup before letting the subscription expire - you can recreate a whole Confluence from that. See https://confluence.atlassian.com/confcloud/create-a-site-backup-724765526.html
The other option is a batch of space exports of the spaces you want to keep - these can be imported into other Confluences as well. Bit more fiddly, but better if you only want to keep some of the data and/or you want to merge it into an existing Confluence
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