Interestingly it had no impact on my score when it disappeared, and I think I know why.
The account was 8 months old when it vanished from my report. My AAoA is also currently 8 months. So the removal of this account had no impact on my AAoA, it was 8 months with this account and it is still 8 months without it.
This proves that the number of accounts doesn't matter to FICO. At least, going from 6 to 7 doesn't matter. It may matter that you have a new account, but I still have other newer accounts. And we know AAoA matters. And it may matter if you go from 2 to 3 or even 3 to 4, thick vs thin.
But other than things like that the actual number of accounts isn't a factor.