As long as your paid account is in good standing, your files are still safe in the McAfee cloud.
Files backed up from free accounts remain in the McAfee Online Backup cloud for 30 days while no backups are occurring. You can upgrade from free to paid at any time. If that is not possible, as long as a second computer succeeds in backing up on that same free account, files from the computer which cannot backup remain in the McAfee cloud.
To troubleshoot backups which do not start or complete: