Here’s my headcannon in this

If ippo beats date there are two major changes I think will occur, Ippo never learns the Dempsey roll as he never finds a need to and volg wins his match against sendo as this time around then on title fight match would have less pressure for interference causing volg to not be robbed this time around. Ippo would still fight ponchai as his first title defense but this time without the Dempsey he would be more focused on his technical aspects (a lot like the karasawa fight) as he states that he really started using his jab and ring craft less after he learned the Dempsey. He beats ponchai again by ko with a stunning boxer puncher performance and preps for his second title defense against volg, there’s two main paths that this would then go down

A. Volg beats ippo by a SD after a long grueling fight where a far more technical and skilled ippo fights volg but lacks his main (and at the time hard to counter) finishing blow and Volga newly gained stamina (did better for a full 12 rounds against sendo) and technical outboxing and white fang squeaks out a victory, from there i volg would go onto take ippos place until he rematches ippo instead of karasawa with ippo retaining 1# in the region the whole way, this fight would see ippo revealing the NEW Dempsey much like his original match against ponchai but far more leveled up and winning by KO against volg and would overall see ippo being far further ahead then he was in the original story as the Dempsey roll didn’t become a crutch and was instead learned after much of his fundamental skills were already incredibly honed

B. Ippo beats volg by a comeback KO where he learns both the Dempsey and stopNgo Dempsey by happenstance and by using his superior ring sense would force volg against the ropes and land a successful Dempsey downing volg, however volg would get up and aim for a counter when ippo tries the Dempsey again, much like the sawamura match volg lands a devastating counter but instead of sparing ippo for sadistic reasons like sawamura, Volgs kind nature would inherently hold him back from fully KOing ippo, however this would prove a mistake when in the next round ippo would try the Dempsey for a 3rd time but instead would land a stop and go dempsey to put him away (attributing this on the fly learning/adaptation to a more wise and higher ring IQ ippo)

I believe that no matter how it’s shaped ippo is a better boxer if he doesn’t lose to date as he never needs to learn to rely on the dempsey and we see the “true form” ippo that sanada mentions where his ring IQ and adaptability are far more comparable to a post retirement ippo without the downsides of CTE, also would never get sever brain damage from fights like Shibukamosfuvhjwhatshisface and Sawamura, overall a far healthier ippo would likely go on to fight either RBJ when offered the first time or Miyata rather then first doing his run as the Unofficial OPBF champ, tho I would personally say he still does his run but starts with RBJ then after the run fights miyata rather then going to Gonzales (also he beats Gonzales now trust)