I could totally see Gandalf still being in middle Earth. He cared about his mission because he fell in love with middle Earth. Had he not been elevated to Gandalf the White explicitly to compete his task reminding him he doesn’t belong there, I could very much see him having gone the way of Radagast, being a force for good in middle Earth for a long time.

Saruman, for all his faults, was correct, Gandalf’s love of the haflings and the good of middle earth was making him complacent.