The realistic risk is convincing scam messages rather than direct financial fraud, because no payment details were held in the affected system.
Someone holding contact and donation records could write a message that looks genuine, using your real name and mentioning a real donation or event. Be cautious about unexpected emails, texts or phone calls, particularly any asking you to click a link, log in somewhere, or make a payment.
SCA UK will never contact you unexpectedly to ask for payment, bank details or a password. If someone does, claiming to be us, it is not us. If you are unsure about a message, contact us using details you already have rather than anything supplied in the message itself.