He might. But personally I think the "don't overstay your welcome" at the beginning of Elbaph was referring to the giants famous temper and something related to Shanks. At the end of the day its still an island allied with Red Hair, and the straw hat grand fleet (well, barto) opened hostilities against Shanks. If he trains Luffy, it wont be as a straight training arc, but as a trial to overcome. So if he rolls up, he might save Luffy only to formally declare war and have the warning come to its conclusion with the giants chasing the straw hats to sea