How risky are 1031 exchanges?

[Matt Foster]

I understand the long term plan on 1031 exchanges are essentially defer, defer, defer, die.  But what happens if you defer, defer, hiccup.  Let's say you're on the 3rd or 4th exchange and for one reason or another the property you have lined up doesn't close therefor leaving you with 3 or 4 capital gains to pay the IRS.  Does this scenario happen frequently?  Are there other creative ways to safeguard this wealth strategy?  Trying to weigh the pro's and con's before I put my strategy in play here.  Thanks in advance.