The following scenario occurs:
- Alice takes the Ready action to do something at a later time (the specifics don't matter).
- An enemy casts Hold Person on her, she fails the save and is now Paralyzed, and thus incapacitated and therefore she cannot take actions, or reactions.
- By some means the enemy concentrating on Hold Person loses concentration.
- Whatever Alice wanted to react to, occurs.
Disclaimer: Alice's turn has not come up again, and so she has not lost her readied action.
Can Alice still use her reaction to take the action she had readied, even though she was incapacitated after she had readied it?