I think this is a case of Chinese whispers, and the meaning has been incorrectly inferred from statements paraphrased in media down the years.
Rather than ‘there’s no way she could have survived’ (inference: a horrific ordeal), I suspect it alludes more to ‘based on our corroborative evidence implicating CB in MM’s abduction, we think there is no chance she could have survived’ (inference: statistically speaking).
Because the odds of survival after abduction by an unknown paedophile are well known to be vanishingly small.
“We have no body and no DNA but we have other evidence. Based on the evidence we have, it leads to no other conclusion.
“I can’t tell you on which basis we assume she is dead. But for us, there’s no other possibility.
There is no hope she is alive.”
Prosecutor '100% convinced' suspect abducted and murdered Madeleine McCann