I remember playing this pack on Custlemm a very long time ago, and I was able to solve the last level that time, so it should still be possible in Neolemmix. It's just really difficult and certainly the hardest one in the pack.
Just solved Forgive Me in Neolemmix, so this is a confirmation to Proxima that all levels in this pack are possible, both in its original form and now Neolemmix. This simply means you have yet to find the solution, mantha.
My solution has a digger left over. This right here is my hint for you on how to use the blockers so that you will indeed have enough builders for the end part. Also take advantage of the fact that you can lose up to 16 lemmings on this level!
If you still can't figure it out, let me know if you need a replay.