> I coud not apply patch:

I was afraid it won't.  I'll attach my current version of longlines.el,
please try it.  If the byte-compiler gets you an error I have to find
the version of this in emacs 22.1 and patch it.  But that version has
some other bugs in this context, hence it's maybe not reasonably to use.

If you want to fix that manually: FWIW the bug is caused by the fact
that before reverting the buffer longlines-mode wants to remove its
newlines.  At this time your file has already changed on disk, Emacs
notices that and tells you about it.  By binding `buffer-file-name' and
`buffer-file-truename' to nil while removing these newlines you should
be able to trick Emacs into believing that the buffer is not associated
with any file and so not ask any questions.

Sorry, it's a never-ending story with this problem.