When a demolisher dies, in addition to the mineable contents of its remains, most tiles below it will convert to slow walkable ground, including filling lava.
Mods introducing new content into the game.
New ways to deal with enemies, be it attack or defense.
Changes to enemies or entirely new enemies to deal with.
Baby demolishers from Demolisher Agriculture do currently not fill lava. I suggest to support them too. The entity name is 'baby-demolisher'.
Good idea. I'll look into it next time I'm working on this mod.