Since our discussion shows that there is no solid and bullet-proof
solution for killed buffers problem (IMHO), I would like to propose
an alternate (less effective, but safe) solution: when the window
dies, it's prev_buffers and next_buffers are set to nil, but both
buffer lists are saved in struct saved_window just for the sake of
possible resurrection. Martin said that the most of window-configuration
objects are created with 'save-window-excursion' and so they're
short-lived objects which tends to not survive next GC. So, if
deleted window isn't recorded in window-configuration object or
such an object dies quickly, we're lucky; otherwise, the only thing
we can do is to hope that recorded window will be resurrected and
Lisp code from window.el will take care about the contents of
it's buffer lists.

Dmitry