We study the entanglement dynamics of $n=2$-, 3-, and 4‐qubit Bell-type and Greenberger-Horne-Zeilinger (GHZ)‐type states under an amplitude‐damping channel (ADC). We quantify multipartite entanglement using the genuine multipartite concurrence (GMC) and evaluate its utility through the optimal teleportation fidelity. For two-qubit states, we analyze the standard (Bennett) teleportation protocol. For three- and four-qubit states, we study controlled quantum teleportation (CQT) with one and two controllers, respectively. Entanglement sudden death (ESD) denotes the abrupt, finite-time disappearance of entanglement caused by decoherence in contrast to asymptotic decay. To counteract ESD, we apply local not (${\widehat{\sigma }}_x$) operations on $m$ of the $n$ qubits ($m\le n$) and derive analytic formulas, revealing that a single-not operation often suffices to alter ESD into asymptotic decay when handling GMC. In contrast, teleportation fidelity can decay more rapidly for single-not flipped states, whereas flipping all qubits is more useful for preserving teleportation fidelity in certain regimes, highlighting that the amount of entanglement alone does not guarantee teleportation utility. Remarkably, in the case of GHZ-type states, ADC-evolved mixed biseparable states can be exploited successfully in the CQT protocol. Further, using the GHZ-symmetric parametrization, we map the two- and three-qubit ADC-evolved mixed states onto a $(x,y)$ plane, revealing their stochastic local operations and classical communication entanglement classes. We also explicitly check the Bell–Clauser-Horne-Shimony-Holt nonlocality hierarchy in the two-qubit teleportation alongside localizable-entanglement diagnostics for three-qubit CQT. Our results clarify the distinct roles of global versus localizable bipartite correlations and suggest simple, experimentally accessible unitary controls for preserving useful quantum resources in noisy channels.

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• Quantum correlations in quantum information
• Quantum correlations, foundations & formalism