Are we already missing some of the greatest minds of our time? The exceptional, brilliant innovators, entrepreneurs, scientists and artists that made life better for us?
For instance, without Steve Jobs, we are not getting any more new tech gadget innovations. he gave us the iphone and ipad and since his death, nothing new. The tech industry has stagnated.
With Stan Lee dead, are we no longer going to get any more great super hero movies? With no Michael Jackson, there have been few to take his place in the music industry to dish out great songs,
and with Steven Hawking missing, we are not getting any new Physics theories to help better understand our universe.
Perhaps will someone one day replace these exceptional individuals or are they irreplaceable?!
Don’t leave the Duke out, John Wayne.
Or
Paul Tudor Jones, who is still breathing and trading.
Some geniuses passes and new ones are born and take their place in history.
I agree with @mlawson71! 
I’d like to stay positive and think that the geniuses of this time are yet to be born or discovered. 
Elon Musk, do you consider him a genius of our time?
The revolutionary people of our age (if not yet in the public eye) will always fill the void left by others, I think.
Hey I am still here, and _bob is on Twitter so that has to count for something. 
The Ever Titanium Laden VIPER
He is still alive, isn’t he?
Alive, but not so well me thinks.
Welll, Mr Musk’s Genius is in “manipulating for dollars”. Now think about this, oh and here comes the physics, but don’t worry you will not see any “scary” math here, maybe.
For an electric car to be practical, let alone successful, it needs the following. A Battery, “better said a power source” the size of a car gas tank, the weight of a car gas tank, annnnnd have the same potential energy of a full “gas” tank. Also it needs to be recharged/fueled in about 5 min. Of course it needs to have a 400 mile range. Also if you are charging it from anything other than Nuclear, Solar, and Wind, it will pollute as much as a regular car running on Gasoline.
Now, the reason I start with Tesla will be evident.
Mr Musk made his Bones by coming up with PayPal, but after that, he is like a young kid who has saved his lawn cutting money and is spending it in a fireworks store in S.C. But Elon has taken it to the next level, he has convinced the local Mayor, and city counsel and his neighbors to give him even more money to buy fireworks with.
Yup that’s it, yeah the concept of an electric car is cool, I really think the boosters landing back on a landing pad, and also being remote controlled, really really cool. The hyper loop, should be called the Hype loop, and the brain implantation deal, yeah well, none of it is profitable, and looks like, well a kid with a couple of big boxes of fireworks.
Now, had he started to build and successfully implement a MSR or Tokamak. Or possibly involved with SSC in Texas, well then yes, genius on the cutting edge, but T Edison and N. Tesla, he aint.
The Never Impressed By Tech Gurus VIPER
Who replaced Leonardo da Vinci ? Aristotle ? Einstein ? (Well I suppose one could point to Hawkins here)
There are plenty of exceptional individuals around - but these days - original thought tends to get penalised and demonised by the “Groupthink rioters” - who espouse the fictions that modern society is more and more dogged by.
I postulate that @sprotz is probably right. - No matter how obvious the truth might be, it will never be allowed to speak it’s name out loud in the face of those who wish to control and demonise everyone else ! (The other day I had teh misfortune to be told by an evangelising vegan that "some people eat dead animals" !
When the whole of your life is invaded by such dogma, what time is there left to be original ? (I saw today a proposal that "obese people “SHOULD” have to pay more to fly on aeroplanes.)
In some ways Elon Musty is a case in point - good idea at the right moment - well executed with a bunch of others and now as TV says - “Out playing with fireworks” - Time will tell on that one.
I don’t think it’s about someone replacing any of these people, it’s more about who will become irreplaceable in turn. Such people are born and florish periodically, only history will tell who will be the irreplaceable people of our time.