> And what do you suggest to do if the frame at RHS is not live?

Sorry, what is RHS?  As far as xdisp.c is concerned it simply must not
set selected_frame to a dead frame.  Never ever.  As far as frame.c is
concerned, it should do something like in the attached patch.  In the
worst case this might make it impossible to remove a specific frame but
this can usually be fixed by C-x 5 2 followed by C-x 5 1 unless things
are awfully broken.  But at least this is a place from where to continue
investigating.  I have no better idea.

 >> I have no idea whether these could help in any way but since we are in
 >> redisplay and the selected frame has become dead all of a sudden ...
 >
 > Why do you think this is a problem for redisplay?

I didn't say that this is a problem for redisplay.  What I wanted to say
is that your fix which is supposed to handle a (maybe only temporary)
problem inside redisplay might cause more serious problems when
selecting a dead frame outside of redisplay.  But maybe I'm confusing
things.

martin