Cannot installworld, don't expect to...Workaround?

I've a not-complete-installworld from today, dumped core halfway through 
despite single-user mode...

began with an install of libc++... which was fine.

i can restore
/lib
/libexec
/bin
/sbin
/usr/bin
/usr/sbin
from an earlier backup

and most binaries work again, but nowhere near
full functionality...   wanting to restore browser
functionality... which mysteriously broke (all segfault) which
prompted the buildworld.

setting COMPILER_TYPE results later in
sh: cc; not found  during the installworld.  
OTOH some buildworld 
produced files may have been lost during the fsck to lost+found

I noticed a few clang files ended up in lost+found during one of the many fsck.

So as an aside of any usual question...
Is there any documentation 
where make installs should proceed?
for instance libc++ first, then ...

and/or how to run the installworld segment-at-a-time to find the
specific failure?  OR it is too complex

Assuming "no" to each of the above...  is there a best
practice to 
copy a greater number of the /lib, libexec from 
backup to completely restore, or is it necc. to
do a reinstall to an ENTIRELY new disk... given that
the existing disk for some reason does not want to
complete it.

Maybe even someone has an easier way... or procedure.

Thanks.

...
As an aside, a wanted feature:

during one disk crash recently, the pass* in /etc wound up in lost+found.
No login resulted.  Restored from backup by luck... was clueless.
Would it be wise to build redundancy into the base, so that for example
if /etc/fstab has vanished, its shadow copy in  /etc/shadow/...
or even enough binaries, (similar /rescue ) to complete a complete svn
buildworld installworld as a sort of /rescue/usr/src with all binaries and
libraries contained therein.

Maybe...