lucy24 - 4:36 pm on Oct 1, 2012 (gmt 0)
4) Return a 410 for these pages and make a custom 410 page with information targeted at people who know what they're looking for. Only feasible of course if those 1000+ URLs have some unfying element that lets you collect them all into a single 410. For example if you've changed from long messy URLs to short pretty ones: then a simple look at THE_REQUEST (or, ahem, IIS equivalent) should do it.
One site I visit regularly has displayed a "we're remodeling" page for several weeks now. Fortunately it's got a Search function that works-- at least for the specific column I read there.