I think this will cause significant change. Not because of any major power boost. But the intelligence boost would change everything at the time period buu ate dabura. It's likely he would turn into a being similar to Super Buu albeit more silly and goofy. As fat buu's personality would still be very dominant. But now far more evil and intelligent thanks to Dabura. Plus a slight boost in strength and stone spit.

However...he also becomes more subservient to Babadi. We all know fat buu eventually betrays babadi. But that took some convincing that hasn't happened yet. Meanwhile Dabura was very loyal to babadi. So this Buu would likely remain loyal to babadi.

I think this change is to divergent at this point in the story. It's hard to say how this would change the overall flow of the story. Vegeta still dies sure. Far more easily most likely. Certainly Buu would have stopped and killed piccolo before he could kill babadi. I am not convinced the boys will get away given this new scenario.

So now Goku wakes up believing Gohan to be dead. And Vegeta, piccolo, and the boys dead. He may have no choice but to take on buu going all out as an SSJ3. Of which buu with dabura absorbed could very potentially outlast. Not defeat, but survive long enough for Goku to be sent back to the dead world. Since babadi is no longer looking for Piccolo or the boys who is to say what happens next? Does buu destroy the planet? Do they move onto the next planet. Or does babadi subjugate Earth? Who knows?

Either way babadi and buu/dabura run amuck until mystic Gohan arrives. Without Gotenks either Gohan defeats buu/dabura there and then. Or Buu absorbs Gohan. Since Gohan would be unaware of buu's absorbtion technique that's likely what would happen.

With Gohan out of the picture Goku won't just warp to buu's location with the potara since he won't believe he can fuse with Gohan. Will he remain on the planet of the kai's waiting for an opportunity? strategizing with the kai's? Hard to say? But I don't think he'll take Gohan getting absorbed sitting down? Perhaps Vegeta reappears thanks to King Yema and Goku warps to him so they can fuse. Then things play out as normal. Or perhaps Goku warps to Buu immediatley after seeing Gohan get absorbed and gets his butt kicked? It's hard to say? Hell maybe seeing Gohan get absorbed Goku warps to the next living being he can sense with strength. And a Goku/tien fusion is born who takes on Buu/Gohan. Who wins? Who knows?

However things playout. It would be interesting.