I\'ve been using Google Wallet for handling our subscriptions for some months now.
Everything seemed to work fine but I just found out that Google Wallet does not send subscript
It was broken (at least in sandbox for me), but is now working again. You should get a SUBSCRIPTON_CANCELED failure postback if/when a user cancels his/her subscription.
My Sandbox buyer (I cancelled a subscription as a buyer) and got an email: