McCarthy was influencial at times last season, not for his work rate, but for the amount of goals he scored. When he scored 24 goals in the 2006-07 season, McCarthy was still not hardworking as he is simply not that type of player, but there is still no question of his class and quality. Him and Roberts formed a decent partnership at times last season (especially at Ewood around Christmas time) so to let McCarthy leave would be ridiculus.
Also, on Sky Sports News a few weeks ago, they were showing which strikers in the Premier League had the best conversion rates last season. Owen was first with a 0.29 conversion rate with McCarthy second with 0.28.
McCarthy can't last ninety minutes but he grabs goals and that is what Rovers need.