Hackers have already figured out how the respawning mechanic in Fortnite is going to work after several feeds release a big datamine find. The image below comes from FortTory, which seems to be getting the most traffic on the situation, showing off a file called "Second Van Change", along with a photo of what the van looks like. As you can see from the image they took, there's a framed silhouette of a body on top of a van, showing that these specific looking vans will be where you can bring players back from the dead.
— FortTory – Fortnite Leaks & News (@FortTory) March 1, 2019
While we haven't seen it in full effect yet, it looks like it will be a direct copy from Apex Legends to a degree. Looking at the files and how they're called "Second Chance", it appears you'll drop a card when killed for your teammates to pick up, then they have to take it to a van in order to respawn you. Just like picking up your banner in Apex. There's nothing to indicate when this will drop in Fortnite, but if they're already this far, it's only a matter of days before they go into testing.