One of the more stressful early game hurdles in Deathloop is managing your meager inventory between runs. Even after you acquire the ability to infuse items with Residuum and keep them in your inventory permanently, there’s an odd sense of impermanence to them. Furthermore, while it is clear that infused weapons and slabs stay in your inventory after you die, Deathloop doesn’t clearly communicate whether the same is true if you deliberately drop them or swap them out during a run.
If you have been wondering about this, you can rest easy: all infused weapons and slabs in Deathloop are permanently preserved in your inventory. If you drop them during a run and leave them behind, you will lose the ability to use them only until the day resets. At the start of each day in Deathloop, you have all infused weapons and slabs returned to your inventory, regardless of what happened to them the day before.
In fact, in order to farm as much Residuum during your runs, you should drop infused items without hesitation and replace them with new Purple and Gold weapons you find along the way. That way you will always return to the tunnels with fresh items to either infuse and store in your inventory or scrap for extra Residuum.