If Mama's Family had stayed on NBC for say 6 years... Do you think the characters and show would have still evolved into what they all became in the syndicated episodes?

If you notice, season 2 on NBC is much more light hearted than season 1 which basically had a lot more intense fighting and family drama. Season 2 seemed to be veering more into the direction of the style of the syndicated episodes... I just wonder if that would have continued... would we have eventually gotten Iola and Bubba?

Maybe not exactly into what they became in the syndicated years, but I think the characters definitely would have evolved and the cast might well have changed too. Rue McClanahan never was happy as Fran from all reports, so I couldn't see her going the entire run of the show if it went for as long as six seasons. But in that case, she probably would have been written out rather than killed off.
The timing might also have been such that she still could have joined the Golden Girls in time for its premiere in the fall of 1985 had the contract situation allowed.
As far as Buzz and Sonya are concerned, their storyline might echo that of Bubba. Heading to college and then out into the real world and either continuing to live at the Harpers or moving out but still popping in.
I personally never cared for how Vint and Naomi were dumbed down. I vastly prefer their characters from the NBC years, especially Vint. At the same time, I prefer syndicated Thelma to NBC Thelma.

Second-season Mama led into syndicated Mama well. I didn't mind Vint dumbed down a bit from season 2 (where he was dumbed down some from season 1); I was more perplexed by the change in Naomi, starting in the second half or so of the third season and really taking off in season 4 and thereafter, particularly with the change in her voice.

if the show had stayed on NBC, we may have seen Iola and Bubba, as Fran and the kids may have left/been written out as it was.

Yeah... I also think Fran would have left at some point still. So we might would have gotten Iola, as someone to fill Fran's spot as a "foil" for Mama. It's hard to say if Buzz and Sonya would have left or not...if so, perhaps Bubba would have come along. We would have probably gotten a few more guest appearances from Eunice and Ellen.