Canceling an old credit card

I’m an authorized user since early highschool on my dad’s Amex plat, I’m 33 now. It’s easily my oldest longest (highest?) line of credit. Since my dad doesn’t really travel as much anymore he’s going to cancel his card.

Wondering how this will affect my credit, I am only an authorized user? And what I should do, is it even important to keep a good credit score, I don’t plan on buying a house, maybe a car in the next few years if mine puts out. I’ve always had good credit I assume bc of this long history on the card.

I read an option is to downgrade the card (my dad doesn’t want to do that) but I wonder if I can downgrade to gold if I’m not the primary card holder?

He also may add me on as an AU on a different Amex card with no AF he has if it would help.