It would of only Delayed the fight, Padme wouldnt of gotten killed as Anakin wouldnt of been angry enough cause Obiwan wasnt there, Anakin would of Told Padme to go away after her long speach about him changing and becoming evil.
It would change everything though, Anakin wouldnt be Mechanical and he would be the strongest thing ever most likey.
There would have been nobody to stop Anakin, he may of even killed Padme before she gave birth. Also he would have never had to wear the Darth Vader suit. By that point he had already killed many of the Jedi. He was already evil.
He would of Fighted with Obiwan but on another planet or somwhere else, Obiwan would of went looking for him to really see what happends then they would Fight..
but if obi wan didnt follow padme to mustafar I think Padme and Anakin would have reason things out... He loved her and did it partly because of her...
Even if they teamed up against palp, obi would eventually be killed. If against dooku he didn't make a difference what makes you think that it would be different against Palp ? You are delirious....
It would have made a difference against Palpatine. He was having a hard enough time just fighting Yoda. If Obi-Wan would have been there he would have at least distracted Palpatine long enough for Yoda to kick his ass.