How common were rebellions among those Slavs being worked to death throughout Greater Germany?
Did they have any idea that they were meant to die and would never be released?
Some did, some didn't realize it until it was too late.
The Soviet forced laborers who survived were generally sent to Gulag when the returned (they were selected to go in the first place largely as a method of keeping dissent to a minimum in the rump USSR) while the families of those who died were told that their loved ones had a found a "new home" in Greater Germany, sometimes even including ginned-up letters. Polish salve laborers, on the other hand, knew the score and would sometimes resist or try to escape. This would have been much more common if the Nazis had allowed entire families to go to Germany. That was rare, Usually at least one child, often the youngest, or the Parent's "favorite" (there were plenty of individuals who would inform for a extra 250 grams of bacon or chicken) would be kept on the Plantation as a hostage (which worked both ways, if the "Hostage" tried to act up they rest of the family in Germany would pay the price and those left behind knew it.
One thing that held down rebellion was that, no matter how bad the work was, there was always something worse that you could be sentenced to (miners had a lifespan that sometimes was measured in days, while Soviet "guest" factory workers actually had about a one in five chance of survival). The biggest impediment was, of course, the Gestapo, who had
carte blanche to liquidate anyone who looked crooked at any time.