Don’t worry she’s going to be okay. XD
 
For those that don’t know Luna is an organic mortal. She ages very slowly due to her demi-goddess status. (Same applies for her sister).Lux is inorganic and cannot die.
 
Lux can “die” if Luna dies. This is because his kind die when they admit theipurpose is fulfilled and mean it. Being with Luna and protecting her is his purpose.
 
If Luna where to die a mother via magical spawn (Lux can’t reproduce) he would still have a remaining purpose to be a father and won’t die until his spawn dies.
 
Contex:
 
So Lux’s kind are evil bastards with no regard to organic life forms. They enslave, kill, and experiment on organic creatures on every planet they claim as their own. Luna’s earth is different though, because some of the organic creatures on this planet have magic powers. This is something they have only seen in inorganic life like themselves. It also makes it harder to attack a planet with two ponies who are capable of moving the sun and moon and Vespaluct (their evil leader) is a bit busy and is so used to enslaving that he prefers to go for the easier prey. This doesn’t make the Earth safe from experimentation, hence why Luna isn’t looking so good.