Mobile peer to peer (P2P) computing is becoming a major revolution in computing owing to advances in computing power, network connectivity and storage capacity of mobile devices. Mobile workflow is, however, characterized by the unreliability of mobile peers who can drop out of the network due to sudden loss of connectivity, drained battery and so on, thus making problematic the guaranteed completion of Workflow Processes in accordance with deadlines. Existing research in P2P Workflow Management has not considered the problem of guaranteeing workflow process completion in an unreliable mobile peer environment. This paper proposes a P2P Workflow Management Architecture for the distributed definition and execution of workflows in a grid environment of mobile peers. The architecture is based on the use of proxies, i.e. fixed grid nodes with which mobile peers register and which act as workflow coordinators. Proxies employ statistical reliability measures of mobile peers in order to calculate the redundancy in the number of peers required to participate in a workflow. The performance of the proposed architecture is illustrated in a journalism scenario.