Anything to draw people into the market area is likely to improve sales, and at the moment there's nothing except the market to pull people off the high street.
A lot of people walk up to Tesco from the central area. Their footfall doesn't go past the stalls or smaller shops in the market, so even if what they're purchasing is available, they don't see it.
That's partially because the central supermarkets are pretty poor- ever met anyone with a good word to say for that Sainsburys?, and both Iceland and M&S are shunned by more people than actually use them. None of them serve the 'social hub' role of Tesco on Acre Lane, which is where people meet by chance and stop for a natter.
Maybe Tesco moving back into the market wouldn't change any of that, and the fortunes of the market wouldn't improve, but what other use for the old pub would have a more positive effect?