When Hock locks himself and Emilie Warnock in the room after rescuing her from the prisoners, a leak occurs which leads to an increase in Nitrogen levels. As the air we breathe is 78% Nitrogen, they would not notice the increase and would pass out through oxygen starvation.
It is incredibly unlikely that a space station would so quickly acquire dangerous orbital decay without performing major maneuvers. The ISS crashing into the station suggests the space prison had a higher orbit than ISS, but orbital decay is a very slow process. The ISS can go months without needing an orbital boost as the drag at that altitude is very minimal. Skylab orbited for five years after its final mission without any orbital boosts.
When the station is scuttled via (presumably) nuclear warhead, there is close to no chance that Snow and Emilie would have survived the hail of debris. The atmospheric densities at such altitudes are very low, which means that it is easy to attain high velocities due to the lack of significant drag. Emilie was seen getting hit in the back by a large piece of metal, and for comparison the ISS performs maneuvers to avoid debris as small as 10 cm in size due to the kinetic energy it carries. While their suits may have protected them from burning up in the atmosphere, their distance to the station at the time of detonation makes survival extremely unlikely.
Someone dropping from an orbiting space station would burn up in the atmosphere rather than landing safely. While no space-suit with re-entry capabilities exist presently, when they exit the airlock you can see the suits having some heavy plating reminiscent of heat shielding. Possibly this is being used to explain these futurist suits ability to re-enter the atmosphere safely.