I leave mine up for good.
If someone archives your gallery or "steals" it from another site, you may find yourself blacklisted somewhere you've never even submitted before, but may want to in the future.
I've got pages over a year old and they still pop up in the weirdest places.
I deleted galleries ONCE to clear up some disk space and spent the entire next day writing emails trying to clear my name. I'll never go through that again. A dedicated box is worth it if only for that reason alone.
I'd suggest YOU archive your old galleries on to one page, and then when someone asks "I need galleries for my tgp", send them on to your site.
Just my
