Hi!

I'm working on destruction effect on geometries, this is my workflow:

1) voronoi fracture the geo,
2) remove some pieces,
3) join remaining pieces back to have a single geo.

The point 3) is where I'm stuck. How to join the pieces back? They share the same point positions so technically it's doable but I can't find a solution.

For example is this possible to fracture a cube and then join the pieces back to get the same cube back?

You already have it, the original is not fractured, just use that no? Switch to the original at the moment you don't want the fractured version anymore.
Anyway, about fusing the points, there's the "FUSE" node, but it would just "weld" the points. I think you mean to "BOOLEAN" the parts together, in this case use BOOLEAN UNION with resolve self-intersections checked.