Isn't it possible to eject the fuel / fuel tank if crash is imminent?
Large jets can usually dump fuel but this is something that takes time. It's sometimes used in less urgent situations where the plane can still fly safely, like a landing gear malfunction or single engine failure.
Source: https://www.airliners.net/forum/viewtopic.php?t=1456931
Some aircraft allow fuel dumps but it is a slow process and done at higher elevation relative to the ground.