I have encountered multiple instances of this. Once, the airlines messed up my connections so badly that I did not make it to the conference (which was in a remote region) although I had given myself 48 hours "leeway" for just that eventuality. We ended up setting up a Skype connection (voice only - the internet connection was quite poor) and the talk was well received. I have to say though, that not seeing your audience and gaging their reaction / understanding is a HUGE barrier to effective delivery.
On another occasion, a hurricane caused severe flooding of the house of an academic acquaintance, and he chose not to travel abroad to give a presentation - instead he dealt with the flooding, insurance, etc. He asked me to give the talk for him, and we discussed it at length so I would be able to present effectively. The only problem was that I could not answer follow-up questions: instead I put up the author's email information as the last slide so people could follow up with him directly.
On a third occasion, travel restrictions (funding) required me to stand in for a colleague; while I was not an author on the paper, I was very familiar with the work (from my group) and was able to present and field questions from the audience. That is the ideal scenario.
On no account should you simply be a "no show": that will affect your acceptance at future conferences (even though it is "not your fault"). Everyone understands that stuff happens - but the show must go on. So find a sub - preferably someone you know and trust, with knowledge about your work. If necessary, just call all the other authors who are presenting in the same section - they are likely to understand the material best. And presumably you know some of them from other conferences?