It is not quite like that. Death means that you drop witchfire, which is the "currency" to level up. There is the soft type, gained by killing mobs, and also crystallized type, which is a different permanent reward. You can go back to an area to pick up what you lost. A mission consists of going to an area, killing clusters of enemies, collecting the drops and opening associated chests, then repeating with other sections, finally leaving through an exit portal. Going back to an area respawns everything and puts you back at the portal you left from. While in a mission you can passively research for better weapons/spells. All that being said, I have had a couple of crashes (W11, 7900xtx), so stability is not the greatest.