The coins will not disappear from the floor, but they cannot be attempted to be picked up if under attack. As it takes a few seconds for the monsters to spawn, it is possible to spawn several sets of them before being prevented from picking up the coins. The coins can be picked up by use of Telekinetic Grab. They are not the same as normal coins, being non-stackable and untradeable. Dropping the coins and then picking them up again does not cause undead ones to spawn.