You will have Social Security. You just might receive something closer to the current level of social security benefits rather than a more generous package. Social Security benefits are indexed to median wages, which rise over time. If they just don't increase benefits so quickly system will be fine. Likewise, a hike in taxes which would still leave us one of the lower-taxed industrialized countries would do the trick.

A funny thing is that we have both fear of automation and fear of insolvent social security. If the economy gets more automated it will grow quickly, and it will be easy to tax the additional income to pay for social security---although we may have to use a value-added tax or a higher corporate tax rather than payroll taxes.