"72T" refers to how to get payouts from your IRA before 59-1/2. I am guessing, but isn't your ESOP outside of a retirement vehicle in the first place?
If it is outside of a retirement vehicle, I am thinking you will pay a big tax when you get it (figure that you will be able to keep half of it), and the balance will be yours to do with as you please. It will be after-tax by then. And you can take a piece of it and pay off the bank for the balance owed on the house when you sell it. You cannot take after-tax money and put it into an IRA, Roth or otherwise. You can only put so much in in a given year from money that you earn in that year. The amount is reduced or eliminated for higher income folks and can't carry over to the next year.
If your pay out is taxable, and you want to get out from under that underwater mortgage, this is about how it would work: You may keep $800,000 after taxes. Sell the house and pay off the bank with $100,000. Now you will have $700,000. Maybe it will make 6 to 11% a year (that would be $42k to $77k in the first year), on which you will have to pay taxes again--say at 28% (WAG) (you will have other income), leaving you about $30k to $55k after taxes in the first year. This gives a net annual increase of about 4.3% to 7.9% (unless your portfolio loses money--it happens from time to time, if you haven't noticed). With ups and downs, if you have invested wisely, you should be able to take out about 4% of the original $700k or about $28k per year to spend each year BEFORE TAXES and your pot should outlast you.
If it is inside of a retirement vehicle (e.g., a 401k) right now, then, yes, you should be able to roll it over into a self-directed IRA and take withdrawals under the 72T rule. You won't be able to take a big chunk out to pay off the bank to cover the drop in equity, though. If you try, you will have to pay a 10% penalty on the amount withdrawn, then pay income taxes on the entire amount you withdraw.
If you want to take money out of your retirement account to pay off the balance anyway, $100,000 net to the bank would be roughly $100,000 x 100/(100-10-28) = $100,000 x 1.613 = $161,300 from your IRA, leaving you $1,438,700 in your IRA.
Assume you get paid out $1,600,000 into a tax-protected 401k when you are 45, three years from now. There are different ways to calculate a distribution under 72T, but the Life Expectancy method is the simplest. (I knew someone who got really screwed up using another method and had to go back and revise it because interest rates had changed.)
At 45, your life expectancy is about 38.8 years by the table in IRS publication 590. The way it works is that you can take out 1/38.8 of your pot as it will be on the last day of December in the year you are 45. (When you are 46, your life expectancy drops to 37.9 years more and in that year you can take out 1/37.9 x your pot at the end of December of the previous year.) So, you can take out 1/38.8 = 0.02577 x $1,600,000 = $41,237 in the year you turn 45. And you will have to pay income tax on that $41,237 (but not the 10% penalty, since you would be taking it out with periodic payments under the rule of 72T).
If you paid off the house (see above), your annual withdrawal will start with $1,438,700 / 38.8 = $37,080 the first year, before taxes.
John Greaney has a very clear description of how 72T works here:
Retire Early: Can I withdraw money from my IRA before age 59½ ?
$1.6 million ain't what it used to be.