No, don't fire them, but I would switch the dressage, xcountry & jumping riders to AD. consolidate the level 1 horses under one rider. The level 2 horses as well.
I'm so glad you found them! Keys are so bloody expensive nowadays, yeah. It's like $12 just to buy a blank key that's not even specialised or anything X)
I am very happy because they'd be expensive to replace haha; I have never in my life lost keys before, and to lose them at 1:30 am trying to go home is not fun xD