I'm skeptical of those numbers, but I might be missing something. It's hard to find anyone actually showing their work on this.
I'll take a swing at it. I don't think this is entirely correct, but at least it's something to point at.
The core of the whole thing is the "Cap Benefit," which is the cumulative difference between the contract's cap hit and actual salary. This Net Benefit is highest right as the relationship switches and the cap hits are higher than the actual salary, but beyond that the CB turns negative and the Net CB declines until it hits zero at the end of the contract. So Parise retiring at the inflection point in 2021 would incur the worst penalty, while retiring near the end of the contract in 2023 wouldn't be all that bad.
With all that said, here's my crack at the numbers.
Season | Age | Salary | Cap Hit | Cap benefit | Net Cap Benefit | Years remaining | Annual penalty | … in millions |
2012-13 | 28 | 11,170,732 | 7,538,462 | 3,632,270 | 3,632,270 | 13 | 279405.3846 | 0.279405385 |
2013-14 | 29 | 12000000 | 7,538,462 | 4,461,538 | 8,093,808 | 12 | 674484 | 0.674484 |
2014-15 | 30 | 11000000 | 7,538,462 | 3,461,538 | 11,555,346 | 11 | 1050486 | 1.050486 |
2015-16 | 31 | 9000000 | 7,538,462 | 1,461,538 | 13,016,884 | 10 | 1301688.4 | 1.3016884 |
2016-17 | 32 | 9000000 | 7,538,462 | 1,461,538 | 14,478,422 | 9 | 1608713.556 | 1.608713556 |
2017-18 | 33 | 9000000 | 7,538,462 | 1,461,538 | 15,939,960 | 8 | 1992495 | 1.992495 |
2018-19 | 34 | 9000000 | 7,538,462 | 1,461,538 | 17,401,498 | 7 | 2485928.286 | 2.485928286 |
2019-20 | 35 | 9000000 | 7,538,462 | 1,461,538 | 18,863,036 | 6 | 3143839.333 | 3.143839333 |
2020-21 | 36 | 8000000 | 7,538,462 | 461,538 | 19,324,574 | 5 | 3864914.8 | 3.8649148 |
2021-22 | 37 | 6000000 | 7,538,462 | -1,538,462 | 17,786,112 | 4 | 4446528 | 4.446528 |
2022-23 | 38 | 2000000 | 7,538,462 | -5,538,462 | 12,247,650 | 3 | 4082550 | 4.08255 |
2023-24 | 39 | 1000000 | 7,538,462 | -6,538,462 | 5,709,188 | 2 | 2854594 | 2.854594 |
2024-25 | 40 | 1000000 | 7,538,462 | -6,538,462 | -829,274 | 1 | -829274 | -0.829274 |
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(Note that the final Net Cap Benefit isn't 0 because the sum of the cap hits doesn't equal the sum of the yearly salaries. This might be because of the bonus structure in the early years. I don't think it changes things much, though)
So going by this, if Parise retired in 2021 we'd be hit with a penalty of $3.86m for 5 years.
I've also seen references to a "max recapture period", but I'm not sure where that comes from. As I understand it the idea is that this is the max number of years that the net recapture penalty can be spread over. So if, say, the max recapture period is 2 years and Parise retires in 2021 with a net benefit of $19.3m, the cap hit would be ~$9.7m for 2 years. I'm not sure if this is really a thing, though.
Smart people, point out what's wrong here.