Quantum immortality sounds exactly like the mythical hell: living forever in perpetual agony, unable to die and in your own branch of existence separate from everyone else you ever knew.
What if we can hack quantum immortality to force continued good health, and the mutual survival of our loved ones in the same branch of the universe as us?
It seems like one would "simply" need a device which monitors your health with biosensors, and if anything goes out of range- it instantly kills you in a manner with extremely low probability of failure. All of your friends and family would wear a similar device, and they would be coupled such that if one person becomes "slightly unhealthy" you all die instantly, keeping you all alive and healthy together.
We nearly have the technology to build such a thing now. Would you install one in your own body? If not, why not?
Who wants to invest in my new biotech startup which promises to stop all disease and human suffering within the next decade? Just joking, there is a serious technical problem here that makes it considerably more difficult than it sounds: for such a device to work the probability of it's failure must be much much less than the probability of your continued healthy survival. You also never get to test the design before you use it.