Probably won't catch him, but I wouldn't be so sure about not coming close.
Say he gets 20 this season (whihc is prefectly possible, given that it looks like he'll be played up front, and pretty much all the time too). That leaves him 55 short.
Andy Cole left United at the same age Rooney would be then - 30. He went on to score 51 more Premier League goals for other clubs.
Not that I'm saying Rooney will be off in a year too, but if he stays that should only increase his chances. Could quite easily pick up 50 in 3 more seasons at United, leaving him needing 25 in his "dotage" - three more seasons at 8-10 a season and he's there.