If you die during a Diablo 4 PvP fight and you're in Hardcore mode, you're dead for good.
We've known normal deaths, that is, deaths that occur during PvE battles, would result in permadeath, but now we know you'll need to start a whole new character if you die during PvP battles in Hardcore mode. Diablo community director Adam Fletcher revealed as much on Twitter.
Permadeath. https://t.co/ZxRz4eE5GXApril 20, 2023
Honestly, this is the way. If you're opting for a mode that makes it explicitly clear that any deaths you suffer will be permanent, there's no reason for that same inherent risk not to extend to PvP. It was that way in the first two Diablo games, but Diablo 3 changed that with its segregated battle arena fights, which notably don't result in permadeath for the loser. Diablo 4, as its darker, grittier atmosphere might suggest, is a return to true hardcore PvP, and folks seem generally delighted to see it.
Today's lengthy developer livestream also revealed another Diablo 4 open beta happening from May 12-14, giving you (presumably) one final chance to play the game ahead of its full June 6 launch. All of the Diablo 4 beta changes revealed so far will be in effect in the May beta, so you can see for yourself what's different from the last beta weekends. Furthermore, the Diablo 4 beta rewards will once again be available to earn by reaching various milestones.
In related news, Blizzard also said today that Diablo 4's PvP zones are "not a place for honor" and won't protect you from bigger squads.