Where can you find player action settings?despawn? or they just shouldn't drop at all?
If you don't want them to fall there is a setting in player action.
If you want to despawn after a certain time period, maybe storing the death location to "%player%_death-location" and then select entity near location, delete. Tho this method isn't something i would suggest doing in a game.
You have to enable it. You won't drop any items and you'll keep the inventory. Make it on join for the most efficiency. Also, don't forget to set items if you're making a game such as a Kit PVP where they're not supposed to drop items, but also not supposed to keep them.I tried to disable keep inventory, but the problem is when I die I still drop items.