Banged frame: Is it still safe to use?
Unfortunately I think that level of damage with a big dent and buckled top tube will make the bike dangerous to ride. There's a chance that when a big bump  or pothole is hit the top tube will fold and dump the rider face first into the road.

Additionally, the head tube probably is not aligned with the seat tube anymore, which means the wheels are misaligned which will negatively affect steering.