This work addresses the general problem of making Network-on-Chips (NoCs) routers totally self-healing in massively defective technologies. There are three main contributions. First, we propose a new hardware approach based on Built-In Self-Test techniques and multi-functional blocks (called Universal Logic Blocks, ULBs) to autonomously diagnose permanent faults and repair faulty units. ULBs have the capability to assume the functionality of various functional units within the router through simple reconfiguration and thus enable the repair of multiple permanent faults within the NoC router. Second, we propose a new reliability metric and introduce a probabilistic model to estimate the router reliability improvement achieved by the protection circuitry. Third, we compare our architecture to two router architectures (Vicis and Bulletproof) and we show that our design provides superior reliability improvement especially in extremely defective nanoscale technologies (i.e., typically above 30% of faulty routers). The most striking result is that the self-healing of the routers enables maintaining the communications at fault levels, where it is normally impossible to preserve communications.