You can cast the exiled card if the token that attacked is still in combat, if it's left combat, if it's left the battlefield, or even if combat is over
(It might, however, be a duplicate copy of the card, as long as you keep the other rules about deck construction in mind.) The opponent is a goldfish, with a deck of nothing but basic lands, so their cards (probably) can't interfere with you at all
As the first enchantment creature, it would have been nice to have it show up in the block that "introduces" enchantment creatures
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On the other hand, if they're removed from combat without leaving the battlefield, use their current information to determine that they're not attacking you or a planeswalker you control anymore