  In the hot intracluster medium (ICM) in galaxy clusters, plasma
microinstabilities may play an important role in the transport of heat and
momentum on the large scales. In this paper, we continue our investigation of
the effect of whistler suppression of thermal conductivity on the
magneto-thermal instability (MTI), which may be active in the periphery of
galaxy clusters and contribute to the observed turbulence. We use a closure for
the heat flux inspired by kinetic simulations and show that MTI turbulence with
whistler suppression exhibits a critical transition: for modest suppression of
the conductivity, the MTI turbulent velocities decrease in agreement with
previous MTI scaling laws. However, for suppression above a critical threshold,
the MTI loses its ability to maintain equipartition-level magnetic fields
through a small-scale dynamo, and the system enters a ``death-spiral''. We
propose a model to explain this critical transition, and speculate that
conditions in the hot ICM are favourable to the upkeep of the dynamo.
Additionaly, with whistler suppression high-$\beta$ regions are brought out of
thermal equilibrium while the efficiency of MTI turbulent driving is reduced.
Finally, we show that external turbulence interferes with the MTI and leads to
lower levels of turbulence. While individually both external turbulence and
whistler suppression weaken the MTI, we find that they can exhibit a complex
interplay when acting in conjunction, with external turbulence boosting the
whistler-suppressed thermal conductivity and even reviving a ``dead'' MTI. Our
study illustrates how extending magnetohydrodynamics with a simple prescription
for microscale plasma physics can lead to the formation of a complicated
dynamical system and demonstrates that further work is needed in order to
bridge the gap between micro- and macro scales in galaxy clusters.
