Smart cities are witnessing exceptional growth in their connections, increasing the need for LPWA com-munications, i.e. low-bitrate, coverage enhancement, ultra-low power consumption, and massive terminal access. 5G Narrowband-IoT, has emerged to satisfy these requirements. Notwithstanding, it presents limitations in extreme coverage scenarios, where devices can lose connectivity unnecessarily. The addition of Device-to-Device (D2D), thus, connecting out-of-coverage devices with a base station through a relay, is a solid approach for mitigating these issues. More comprehensive performance and sensitivity analyses are required to achieve this goal. This study targets two typical scenarios, urban and suburban, measuring the impact of the duty cycle, path-loss, retransmissions and interference, regarding the expected delivery ratio, end-to-end delay, and the QoS. Our simulations show how the behavior of these quantities leads to a novel strategy to avoid disconnection.