Even if Wallace isn't hit on May 15 1972, I highly doubt he'll make that much of a splash in the later primaries. Best case scenario IMO is that he's hit but only suffers a minor flesh wound and goes on campaigning TR style.
Only 6 state primaries remain post May 15. Provided Wallace survives, he'll surely win Maryland and Michigan like he did in OTL, perhaps with larger numbers. The next three primaries -Rhode Island, Oregon and of course the all important California- I can't see Wallace winning in, increasing his vote % yes, but winning? No. McGovern still wins these IMO. Wallace also probably doesn't stand much of a chance in New Jersey either given his views on Civil Rights.
That being said, New Mexico could definitely go Wallace's way, considering he garnered 29% of the vote there in OTL. Wiki says 100% of South Dakotan Democrats voted for McGovern is that right? Perhaps Wallace could win there as well but it's admittedly a stretch.
At any rate, Wallace's survival means he comes into the convention with a stronger position than OTL, but not by much. It's tough to see the rest of the party rallying behind him of all people to stop McGovern.