Nepean, page-10

You're right. The mine closed in 1987 (according to Mindat), so it's one of the few original nickel boom-era mines that's never had a second or third life. However there were flat-lying granite / pegmatite intrusions cutting off the orebody in a few places, and I believe a thick pegmatite at the bottom of the workings was the cause of the original closure.
Of course that also begs the question as to whether the host sequence continues to depth beneath the bottom pegmatite?

When the aptly-named FML were looking at reopening Nepean the nickel price was over $25,000/t, but by the end of 2008 it had dropped back to $10,000 and they put those plans on hold.