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.
The link to the source code on the mod portal https://github.com/sparr/factorio-mod-demolisher-remains-fill-lava is broken for me, did you make the repo private or (re)move it?
I may have actually forgotten to push it to github. I'll try to fix that when I can.
There hasn't been any further development since the last release here, so you can just unzip the mod here for the latest source for now.