"If we in our sole discretion determine that you have engaged in abuse, misuse, or gaming in connection with the welcome offer in any way or that you intend to do so (for example, if you applied for one or more cards to obtain a welcome offer(s) that we did not intend for you; if you cancel or downgrade your account within 12 months after acquiring it; or if you cancel or return purchases you made to meet the Threshold Amount), we may not credit the welcome offer to, we may freeze the welcome offer credited to, or we may take away the welcome offer from your account. We may also cancel this Card account and other Card accounts you may have with us."

You should still be able to cancel before the renewal fee is due without having to worry about losing miles as long it's 12 months after acquisition (there's a grace period before you have to pay the fee).