Device-to-device (D2D) communication and Heterogenous networks (HetNet) in wireless communication networks (WCNs) are known to enhance system capacity, coverage and energy efficiency. A key area where these can improve the overall performance during partial and complete infrastructure unavailability, and ensure coverage, along with essential information broadcasting is the public safety communication systems. Looking for an appropriate architectural solution for the 5G WCNs and beyond, during an emergency, this paper proposes a two-tier architecture for achieving guaranteed Quality of Service (QoS). Under appropriate availability from the macro base station (BS), public-safety users are serviced by it directly, which forms Tier 1. However, under the situation of loss of infrastructure and/or for offloading public-safety traffic from the macro BS, the public-safety users are serviced by the Tier 2 elements, i.e small cell BSs and D2D links. As far as possible, use of D2D or cooperative communication is braced, as it provides higher system throughput. Also, D2D supports much lower power consumption, thereby making it more suitable during emergency situations where users may not be able to recharge handsets frequently.