When you enter the Nether, you enter Hardcore mode, and when you come back to the Overworld, you're no longer in Hardcore. It's a rather simple mod in terms of scope.
The goal of the mod is to make you stop and think "Am I prepared?" when you're about to step into the Nether portal. This mod pairs nicely with already existing mods such as Unforgiving Void, where if you fall into the Void, you end up in The Nether, Natural Nether Portals, where you can find naturally generated portals in the Nether and the Overworld, and NetherEx, a huge overhaul of the Nether.
If the concept of revival is on the table (multiplayer server), that might be dependent on an external mod such as