If my country gets its population reduced by more than 50% as a commie (say from 100+k pop to 40k pop), but all things being relatively equal (no. of indy complexes remains the same except maybe with a 3% overall reduction and tech levels remain the same) can it cause my indy production to drop drastically?

I was producing 60k+ turrets but after suffering a series of guerilla strikes, I am now producing only 20k turrets, despite the fact that my buildings remain intact and my indy tech level remains unchanged. Is this normal?

yes, yes and it sucks.