What happens to your Pawp access depends on which Pack Membership tier you're moving from.
If you downgrade or cancel from a Gold Pack Membership, your Pawp benefit ends, since continued access is tied to staying on an active Gold membership.
If you downgrade or cancel from a Silver or Bronze Pack Membership, your free trial isn't affected — once redeemed, it continues for the full 6 or 3 months regardless of any later change to your Halo membership.