Handling death counts should be in the Player Controller (Server-Side). Create a Deaths (int) replicated variable. On death you increment that value for the given player.
At the end of the game you look loop the GS PlayerArray (get game State → Get PlayerArray). The player array is an array of all Player Controllers.
Create a Function to return the winner via Looping the PlayerArray getting the Deaths value and comparing it to a local. The locals default value is enormous, so player values will always be lower.
You’ll probably want to consider Ties. Multiple players could have 1 death or 0 deaths.
For matching deaths greater than zero you look at who died last. So each time you increment a death in the controller you’d update a new variable classed Last Death Time (gametime). Your loop would then change to:
((Deaths <= Least Deaths) && ( Last Death Time < Current Last Death Time))
For multiple zero death situations you’ll need another criteria like score to weigh against. Or just use score for both scenarios.