"yes, the flag is still on the moon, but you can't see it using a telescope. I found some statistics on the size of lunar equipment in a Press Kit for the Apollo 16 mission. The flag is 125 cm (4 feet) long, and you would need an optical wavelength telescope around 200 meters (~650 feet) in diameter to see it. The largest optical wavelength telescope that we have now is the Keck Telescope in Hawaii which is 10 meters in diameter. The Hubble Space Telescope is only 2.4 meters in diameter - much too small!"