There are a few reliable ways to kill Terran soldiers without pumping them full of ten thousand energy pellets. These are:
(note that the brain can be uploaded into a new body for no more than 30 days after the body dies, the brain will die off in mere hours after hitting that deadline.)

Electromagnetic Pulse
When within a 150 yard radius of the epicenter of an EMP with over 400 petawatts of power, all nanobots in the soldiers' body will be fried, making him mortal until new nanobots come to replace the dead ones, which takes from 50 up to 200 minutes depending on the environment. An EMP of 1000 petawatts or more will destroy the brain's neural network causing instant death.

Not anymore! Although very heavy EM-radiation still destroys the neural network, the newest generation of nanobots now uses EM for power instead of being destroyed by it. And newly developed AI cores that support the brain functions can now store a person's identiy if the brain is damaged; as long as it takes for the nanobots to repair the neural pathways.

If the soldier is engulfed in a continuous stream of fire, the flames will cause more damage than the nanobots can repair, killing the body in approximately 20 seconds after igniting. Of course, the soldiers' shields and armor have to be down first for the fire to have any effect.

If the body is turned to liquid, it can still be repaired; but that would be in vain as the person inhabiting it will have died almost instantaneously upon liquefaction.

Even the nanobots cannot repair something that doesn't exist anymore.

High-level radiation
When exposed to radiation that amounts to 600 RAD per second or more, the nanobots will start to melt, after which the soldiers' body will start to be affected. First the natural organs will fail, the nervous systems and muscles will then follow. For now, the body can still be saved. (up to 3 hours)
Septic shock usually occurs after 3.5 hours.
Next, the insides of the soldier will be pulpified. This is the point of no return for the body. (after 4 hours)
After 4.5 hours, the brain cells will start to malform and eventually, fall apart, causing delirium or total insanity. Once more than 30% of the brain has been disabled the soldiers is clinically dead, even the nanobots cannot save his life at this point. (death usually comes after 5 hours.)

Some things that would kill any other man don't do anything to permanently harm Terrans.
These are:


Why this isn't lethal:
Even when chopped into a dozen pieces, the nanobots will repair the body as long as the brains are intact.

How this can be lethal: If the brain isn't intact or all nanobots have been rendered inoperable.

Bullet to the brain

Terrans can survive far worse than this... (courtest of

Why this isn't lethal:
While this causes trauma to the mind, as long as the brain doesn't shut down completely it can, and will be, repaired.

How it can be lethal:
If the amount of taken bullets is enough to break the brain into pieces, at which point death is immediate.
Not anymore, even shattered brains can now be repaired, and the soldier will survive just fine.


Why this isn't lethal:
Since the nanobots can make air out of everything, including dark matter and neutrinos, suffocation is literally impossible.

How this can be lethal:
Suffocation is possible if all nanobots are rendered nonfunctional.

Cold base

Most species have trouble living here with heavy insulation and heating. Terrans can go outside draped in ice cubes, whilst eating ice cream and not feel a thing.

Why this isn't lethal:
While freezing damages the organic systems, nanobots are immune to all but the most extreme temperatures. They will keep the body alive and running, and try to unthaw their carrier at the same time. Depending on the situation this may take a few hours, and the frozen person is conscious the entire time. While trauma-inducing, being frozen alive isn't lethal.

How this can be lethal:
Only if all nanobots are rendered inoperable.

Cannot happen anymore, the new nanobots can survive at 1*K.

Dry and hot

Dry, hot, and inhospitable. No problem for Terrans.

Extreme heat

Why this isn't lethal:
Extreme heat isn't lethal because the nanobots will simply turn the hot air into cold air, and will vent their carrier's body regularly.

How this can be lethal:
If the temperature is extreme enough to kill the nanobots  (200.000*F) or all nanobots are rendered inoperable.

Squashing or crushing

Why this isn't lethal:
Because Terrans don't need to have to breath and their organs are unnecessary as long as there's nanobots in their body, getting squished is a painful but harmless event.

How this can be lethal:
Not. Just not. Even IF all the nanobots are dead more will come to take their place. Only if this takes more than 30 days (which it doesn't) will the person actually die.


Why this isn't lethal:
The current will damage the organs, but since they aren't necessary it doesn't matter. The nanobots can withstand any electrical current up to 400 petawatts per second.

How this can be lethal: IT NEVER IS
If the current does severe damage to the brains or if all nanobots are rendered inoperable..