From the article, the only really nasty things are:

  [a].forEach(fn(){})
  [b].forEach(fn(){})
  // Parses as [a][b]

  return
  a+b
  // Parses as return;

You would have to work pretty hard to trigger the rest.

I'm curious about the speed trade offs from removing semicolons. You shrink the source code a little, but does the parser throwing exceptions all the time bump up execution time?

A parser would not normally handle this kind of thing with exceptions, and any cost would only be paid once, at parse time when building a syntax tree, not at execution time. Very few languages interpret text directly, rather than interpreting trees, as the trees are far easier to work with, more efficient, etc.