I think it's probable that if were were to be able to image worlds across the galaxy, or visit them directly, we'd find the remains of many dead civilizations. I mean, we're not that old and we've nearly offed ourselves (or been offed by asteroids or whatever) many times in our history.
As an extension of that topic, for the folks that truly believe there were advanced ancient civilizations on Earth (human or otherwise) the places we should look for them are on the Moon or in extended orbit. The stuff we put on the moon will stay there basically forever because there's almost zero erosion or geological activity. Or in orbit, far out where atmospheric drag wouldn't cause it to de-orbit. So if there was an ancient spacefaring civilization on Earth, that would be place to look for signs of it.
If we could shine a laser beam at dead moons in nearby star systems where habitable planets might have been there, we might just see a return from experiments like the Lunar Laser Ranging experiment, which would probably continue to work for millions of ears after humanity is dead and gone:
en.wikipedia.org