Umm, your pessimistic forecast is way too optomistic
and just plain wrong!
There's an awesome AP article this morning with the headline "Social Security Fund Now Seen To Be Empty by 2037"
People, I've got news for the AP: That sumbich is empty now!
Every penny of payroll tax revenue is spent to help cover current general expenditures. We can't even really say which general expenditures because money is fungible.
Payroll tax revenue is not being saved or invested.
If payroll tax revenue was really in a "lockbox", then it wouldn't count in figuring out the current deficit would it? Well it certainly is counted as general revenue when the government calculates its deficit.
Your payroll taxes do NOT fund your personal social security retirement benefits. Future social security benefits are unfunded liabilities of the federal government, payable out of future tax revenues.