The Cure transference property :)

They don't have to die, it all depends on how long they were a vampire.
Elena won't die no matter who takes the cure from her because she was only a vampire for like 2 years so she'll only age 2 years while Katherine aged about 500 years when Silas took the cure from her.
But if Damon or Enzo take the cure from her and then someone takes it from them, they will die because they've been vampires for 100+ years.


I only dance at the funerals of people I hate

In season 5 Silas had to completely drain the blood from Katherine's body to get the cure. She did die for like a minute but then she came back. But since she lived longer than a natural lifespan she eventually aged rapidly and died after losing the cure. Elena only having been a vampire a couple years would be fine. Silas presumably didn't die oc blood loss when Amara sucked the cure from him possibly because he didn't die to become immortal unlike the vampires, or it just happened off screen. The cure can't exactly ve shared except Caroline, Elena, Tyler would all be able to take it one after another with no consequences since they were only vampires/hybrids for a few years, but after that only 1 of either Damon, Stefan or Enzo would be able to take it because if any of them lose it they'll rapidly age til they reach their true age and die.