They did escape & survive the explosion of the fuel tank and breakup of the shuttle, in the most horrible sense of the word. 

NASA eventually concluded that the explosion of the main fuel tank was not strong enough to kill or even seriously injure the seven astronauts, but it was strong enough to separate the crew compartment from the rest of the debris, sending it on its own course, and the compartment did not start spinning or tumbling enough to induce unconsciousness. There was no evidence the crew compartment suffered an explosive decompression, but it is hard to say that with certainty because of all of the windows & frames were shattered when the compartment hit the ocean surface.

So they escaped the explosion, and likely were alive and likely conscious for the two minutes and 45 seconds it took for the crew compartment to reach its maximum altitude of 65,000 feet and then plummet into the ocean. Estimated impact speed was 207mph, creating an impact force of over 200g. That's the most likely cause of death, no person could survive that. 

It was only about 100 feet of water, so the wreckage buried itself in the sea floor and took about 10 weeks to find, despite having a reasonable idea of where to look.

Between the impact and 10 weeks in the ocean, their remains couldn't be separated and individually identified (one source described them as "gelatinous"), so they were cremated together and interred in a single grave at Arlington. 

https://www.nbcnews.com/id/wbna3078062#.Vs9CCpMrLfY