This page of the guide to Death Stranding answers a very important question - what happens when the main hero dies. This is not so obvious, because you won't see the traditional Game Over screen.
The main character is the so-called a repatriate which means that when he dies, he goes to a place called The Seam. This place looks like depths of a sea. We move as Sam's soul and observe the action from the first-person perspective.
If you play online, then you can optionally search for the souls of other dead players left in The Seam. They are floating corpses to which you can swim up and interact. This strengthens your connection with that player - from now on, you will share more items and structures.
Your main task is to find Sam's body so that his soul can return to him. You can do this yourself by using the scanner or just hold the Repatriation button. The hero will be revived near the place where he died earlier.
If you found the soul of another player under water and made a connection with it, then after returning to the world of the living you will find some equipment carried by that fallen player. You can take this loot with you and deliver it to the allied location or ignore it.
Important information is that despite the free resurrection mechanic, there are still moments where you can see a game over screen. This can happen, for example, if you fail a main order by destroying the cargo or when you exceed the time limit. You will then need to load one of the previous saves meaning that you will have to repeat this section.