If your panel log-in continues to function then you should still be able to log-in and manage your rewards payments. The big question is whether your panel log-in will continue to function once you no longer have an active hosting plan under the account, I suspect it would, but you should ask DreamHost about this to be sure.
Once again, you will need a functioning panel log-in. However, DreamHost does say this on their hosting-rewards page...
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