I think there is no need to "repair whoosh" (or the index).
It might be simply your code that opens a writer, uses it maybe, closes it and then tries to use the closed writer again.
Just always do it like that:
with myindex.writer() as w:
w.add_document(title=u"First document", content=u"Hello there.")
w.add_document(title=u"Second document", content=u"This is easy!")
And if you need to add more documents later (outside this "with"-block), open a new writer the same way...
Note: the writer w gets automatically closed when leaving the with-block, that's how a so-called context manager works.