They can but it is rare, they are not specifically attacked by anything. When they see a nearby enemy they panic and run around randomly.
If so, how do they respawn
You get one for each tile you build and they hatch from the tile without needing an egg for free
Also, the leaf cutter colony is really immersive looking as a whole, with different sizes of ants and majors patrolling near the queen.
It is a big change from what we have already. Resource management is quite different as you need to get leaves take them to a leaf drop of chamber, the minims then take the leaves to the nurseries where they convert pretty quickly to fungus. When fungus is spent it leaves behind rubbish that needs taking to a refuse chamber by the minims before more fungus can grow on the tile.
All in all you are balancing number of minims, size of leaf storage, location of leaf storage, location of nurseries (and quantity to hold fungus), size of refuse chamber and location of refuse chamber. Management and base design wise it is a step up from what we had before.
Then the different sizes mean they can pass through one another making army composition different