After Soyuz 11, cosmonauts have been wearing pressure suits (which is so tight they cannot stand erect inside it). The leak in Soyuz 11 started probably when they were strapped on their seats and undergoing G forces at re-entry so were unable to prevent it. Some have said that putting a thumb where the leak took place would have saved them, but...I wonder about an oxygen mask if that would have been enough too.
OTOH, with Apollo 7, all 3 refused to wear their spacesuit (against Kraft's order) and since, none of the Apollo astronauts returned back with their spacesuits on, even after the Soyuz 11 tragedy.
And about Shuttle emergencies, i feel they train for unlikely contingencies and cannot train for far more likely unsurvivable contingencies. There should be a study about those likely v unlikely contingencies and their chances of occuring and survivability and this would cause some hair raising at NASA, I believe.

Raoul