Will it be appropriate printed quality if use images at original size with resolution 72 dpi in banner 80 cm x 200 cm?
Take the original ppi information and throw it for the window.
The original ppi information does not matter. The question is the original size of the image.
900 x 600 px... for a 80x200 cm print... now that is the problem.
You have a totally wrong proportion.
Regarding the resolution.
600 px across 200 cm are about 3 pixels per cm. That is 3 mm each pixel.
If you can live with that, go ahead. If the image is the only one you have, for example, is taken with an ultra sensitive gamma ray camera (with resolution limitations) and it is the only proof bigfoot was on your backyard, use it. If not, go and find another image.
But the real resolution needs are defined by the viewing distance and the usage intended.
Oh if you have a lot of tiny images, 900x600px at 72ppi at a final size of 32x21 cm yes, 72 ppi is fine.