Dude...that's an awesome idea... O.O
The landscape is totally changed and different, BUT I think it'd be totally possible for old ruins and the like to still exist. I didn't really make it clear on what "destroyed" encompasses (partly because I'm always adding to the game and totally open to new views and interpretations! XD). The cyclical destruction could mean a literal *KABOOM!* Earth is nothing more than galaxy dust, and has to reform right from space particles all over again, or it could just mean some cataclysmic event happens that causes mass earthquakes, lots of plate shifting and volcanos forming new land masses, and wipes out the grand majority of life on Earth. In either case, life has to start over from scratch. ^__^
I thiiink...the latter is a better idea, because then there can be ruins and stuff, and as you said, exploring those ruins could make for some awesome plots and be really interesting! I never even really thought of that before, but yeah, that's an awesome idea, so I think we can go with the latter idea which means, whoo, ruins!
^___^ Ahhh! That's such an awesome idea! <3