I think that from a "business" perspective, we might very well see a "In Memory" graphic at the beginning of every show since he was the owner, chairman, and driving force for so many years, after all. Perhaps an annual tribute show may be held as well, or perhaps an induction into the Hall of Fame (if he is not there before his death). Shane or Stephanie will take over and do their best to run the company on-screen (much like they do now). It will surely be different, but no worse than now, I am sure.
In terms of other federations, it will surely have an affect as they also might have to mention it on their broadcasts and give Vinnie Mac his much-deserved props.
From the personal perspective, I doubt much will change. As colossal as the loss would be to the McMahon family itself, and to all the start he is close to, the world and business would go on as usual. I doubt anyone is going to mention Vince in their promos or anything of that sort...
...but then again, it is possible that only a one night tribute show will be held and then nothing ever again. It would be keeping with tradition along with everyone else who had died in the past... again, surely personally people would grieve, but professionally, the show must go on.
In terms of the industry, I also doubt it would make a colossal impact -- there are other McMahons in like to take the throne, so to speak. And if not Shane or Steph, surely Good Ol' HHH will be too old to wrestle by then, and may be considering a role behind the scenes as the Grand Poombah. Whether they that replace him will be as effective is an argument all unto itself... but life is life and death is death, and not even The Vin Man himself is immune from it. His legacy will not be forgotten, that is for sure, at least by those fans who were around when he revolutionized the industry, and possibly their offspring who are bread with respect for said revolution.
When that sad day comes, I will be in mourning, as I was for the loss of Owen, Benoit, Eddie, Lockwood, Taylor, and others. We will keep them in our memories, and prayers.