Modern R/C equipment is , under normal circumstances,"line of sight"...that is to say.if there's no obstruction between Tx and Rx, they'll communicate.
As Denti pointed out, with the advance in wireless cameras, the ground operator no longer needs to see the speck in the sky.
plenty of large-scale models about but over a certain size, they're subject to CAA regulation.
For those with time to kill, there are many clips on youtube of magnificent models, some big enough to carry a small human!
Yes they can (and do ) kill.