Well this depends. If you mean, the host didn't have the unit active and was about to die, thus the unit removed itself, then... that wouldn't make much sense. When the unit is active, if the host dies it just regenerates them and brings them back to life. So if the host were dying, I'm sure if the unit did activate it would just save their life. So, as sonarelite did, I'll list what I think might happen.
Option A: The host dies but the unit doesn't stop functioning, because even without bio-energy from the host, which it doesn't draw upon when in the boost dimension, it still has the energy within HyperSpace to sustain itself.
Option B: The host dies and the unit auto-activates in recognition of one of its main directives; protect the life of the host. It would probably be a safety feature; if the host's life ends, or the signal from the 'Telepathy Growths' cuts out, the armor will activate in their last known coordinates.
This second one is what I personally believe would happen.