Ultimately, what is deemed to be plausible or otherwise is determined by the filmmakers. If they decide someone or something can live after falling off a tall building, and justify it in universe, then so be it. Examples I can think of are in Superman 2 and The Game.
As far as the techniques used for filming, it varies. Some that I've seen:
Blue/Green screen - Film a person flailing their limbs and screaming against a green screen, and composite them into a shot looking down from the top of a building.
CGI - Animate and render a model of the character falling, and composite them into the shot
Stunt fall - Have a trained stuntperson fall from a great height onto an inflatable stunt bag - filming only the jump and fall, omitting the landing.
And of course you have to show them landing. For that, you just need a separate shot where the actor/stuntperson lands after dropping from a much shorter height. My favourite example in this regard is in Terminator, where Michael Biehn was pushed off a ladder and filmed dropping hard onto the ground as he "travels back through time".