Of the 288 coasters I've ridden, 28 are gone so about 1/10 of the coasters which I've ridden are gone now.
While checking the lists for coasters I've ridden, I saw "Jet Star - Spreepark" in day 1. Spreepark was a themepark near Berlin which was closed about 14 years ago. I think the coaster is still standing in the park but it hasn't been working since 2001. So I guess this coaster should be replaced with a currently operated coaster?