how will the bent tube actually affect the the bike?
It certainly lowers the $ value of the bicycle. It will also, most likely, cause the bicycle to handle poorly. Chances are good that the bicycle, when ridden, will pull either left or right. Hardly a decent quality ride, in my opinion. That said...
If all you care about is basic and cheap transportation, then you have the bike of your dreams. It will get you around, however unsafely, but it will, probably, be rideable.