So, we'll never see our loved ones again?

[Mister Agenda]

But why does it have to revive. Why can't it stay dead?

In strange aeons, that which never truly died can sometimes revive. A truly dead plant can't revive. Some cells at least have to still be alive for the plant to revive from a state of dormancy.

Critters like us are more dependent on our parts working, once the critical ones no longer function, we can't be revived even with a pretty high percentage of our cells still living, though even with us, death isn't quite what it used to be with modern medicine. We use the term 'clinically dead' for someone who shows none of the traditional signs of life (breathing, heartbeat) but is still potentially revivable. What constitutes clinical death is a moving target as we improve our medical techniques and technology to be able to revive people that we couldn't have 50 years ago.