Unfortunately, all characters made during the Early Access and Open Beta weekends for Diablo 4 will be deleted after the beta has been completed. A maximum of 10 characters can be made though, so although they will not be long-lasting, players can enjoy trying out D4 items different character classes and seeing which playstyles best suit each player.
Unfortunately, these rewards and the fond memories of slicing through the plague bearer and demons of Hell will be the only things that will carry forward to the release of the game. All characters and loot will be deleted to clear the way for the updates and changes that developers will need to make with adjusting and balancing classes and other things which may have come up during the Diablo 4 beta.
Although the progress made won't save for players in Diablo 4 after the Open Beta, that doesn't have to be seen as a negative. Come June 6 when the game releases in full, players should be able to enjoy starting fresh and seeing what alterations have been made to the classes and even the area of Fractured Peaks. This period of beta testing gives the development team a chance to see what is working and what isn't, and deleting things in order to Diablo IV items make Diablo 4 the best it possibly can be at release is worth it.