OK, if you haven't got cloud backup, come back to me, I may have other solutions.
Firstly, what do you mean by 'dead'?
When connected to a charger, do you get a light? Anything on the display at all?
If not, try cleaning the port with a clean toothbrush. Then try another cable/charger. It's also worth trying the wireless charging, sometimes it works when the port is broken.
On the phone, hold vol down + home button and then press the power button. Any vibration? Anything on the screen? It should show up 'download mode'. (If it does, you can power off as normal) This is just a test to see what level you can get too.
Report back with the results.
(I will say, these are a PITA to fix, the screen and back panel are glued in place. This normally involves a heat pad and around 85 degrees to melt the glue, before opening the panels. Also, unless you take it back to Samsung, you are unlikely to keep your waterproof rating.)