I've never seen anything in any IRS publication that placed limits on the balance of a 401K, only on what you can contribute (and defer from taxes) each year.
The way the IRS 'gets theirs' as it were is on the taxes you have to pay (for a traditional IRA anyway) which would not be insubstantial when you start to figure out the required minimum distribution if the balance was 14Mill..
You're required to take out enough to in theory run the thing out of money by your life expectancy.. The IRS has tables for this stuff to give you the exact numbers, but for the sake of a simple example, their number for someone age 70 (single or with a spouse who is not more than 10 years younger) is 27.4.. If we round that to 28 to make the math nice, then you would be forced to withdraw and pay taxes on around $500,000 per year. (So there would be a hefty amount of taxes to be paid out for sure).
So a lot of that $500K a year going to pay taxes on your distributions, but then, considering you only contributed 660,000 pre-tax dollars in the first place, what a wonderful problem to have to deal with. Oh don't throw me in THAT briar patch mr fox!