Getting Started Guide
When you die on this modpack you don't respawn. Rather, when you get killed you enter a downed state in which your friends will be able to revive you. But it isn't as simple as just getting to the dead person and reviving them. You first have to brew a Potion of Revivify, which allows you to do just that when used.
The potion can be brewed like this:
The standard version of the potion can be brewed with Mundane Potions and a Golden Apple. There is also a better version which can be brewed by adding a revival star (which can be traded from a Cleric Villager), into Potions of Regeneration lvl2.
Let's say noone is able to come and rescue you, what then? Normally when you die in hardcore you die for good but with this modpack there is still a chance for you to get back to life.
On the server side of things there is a custom datapack that allows for respawning all dead players regardless of them being online or offline. It does this by adding a function which server owners will then be able to execute however they see fit. How this is implemimplemented is entirely up to the server owners.
An example could be to setup a schedule that executes the command at an interval like once every day/week. This is possible with most hosting providers.