Since the Social Security fund is paid for by taxation and Congress can vote to increase the level of tax collected, both the percentage collected on income and the level at which collection stops, it is unlikely the fund will actually run out. In recent times, Congress has voted to increase the age at which workers can retire with full benefits, and raised the amount of earned income which is subject to the tax. There is no reason to believe that when push comes to shove they won't do it again.
That being said, my missus and I have been planning our retirement based on the assumption that Social Security will be either gone or so small as to amount to no real supplement at all.
What most people fail to realize is that Social Security was sold to the public as a supplement to their own retirement savings, not as a retirement plan in itself. It was also instituted at a time when workers rarely lived to be 65 or older so few ever drew much out of what they'd paid in. This was done purposefully as the money collected for Social Security, by and large, was meant to be "borrowed" by the general fund for government spending on works projects. The people who designed Social Security never expected it would ever have to pay out to someone more than they'd paid in over their lifetime. It was also never meant to pay out disability payments and no appropriate source of revenue was ever put in place to counter those expenditures.
The real question becomes, will an agency like the Federal government, which can extort money from the populace at the point of a gun (all taxation is achieved by violence or the threat of violence) allow a program as broad and far reaching as Social Security to go bankrupt, or will it do what it must to sustain it?