Without HFT-
A handful of HFT shops close down. A few hundred MIT/Stanford quants/programmers are laid off. Most retire with all the cash they made stealing from the markets over the last few years.
Thousands of human traders go back to making a great living trading.
Hundreds of small trading and finance companies reopen, hiring back the tens of thousands of previously laid off back office workers.
Small restaurants, deli's, lounges, boutiques, and bars reopen around trading offices hiring thousands of employees.
Public has new faith in markets without computer glitches, flash crashes, sub pennying, quote stuffing, and algo manipulation. Public starts putting money back into stocks.
Wall st. wealth is trickled down throughout the economy.
Unemployment drops, housing values uptick, economy shows first signs of unassisted growth in half a decade.