Yes, I think you will see a drop. 10 years of history is a lot, unless you have other accounts as old (or older) as this one that can absorb some of the loss.
New York Yankees - 2009 World Series Champions. 27... and counting.....
I have 30+ accounts on my reports but due to a BK this would be my oldest TL. Average age shouldn't take that much of a hit and FWIW the mortgage was only open for less than one year to begin with. How much could it have helped me in the first place?