Seems the problem that's been reported about project tabs disappearing
is because of a hosed up iws file. This just happened to me, and
removing the iws file restores everything and you don't lose ALL your
settings just some of them.
It happened while I was working in an XML document. IIRC I was
selecting all and deleting the contents of the document, and that threw
an exception (reported), and after that things started going down hill,
one problem after another. Restarted idea... whap... bye bye tab.
hope this helps others.