Once you have a 241 voucher, do you have to keep the Amex card until you use it? What happens if you move abroad and they automatically shut your Amex account down?

Also, OH's Amex is just shy of the £10k so we are retiring it for now and swapping to mine. Can I 'attach' my Amex card to his paypal top up card, or do I have to open my own? (We have different surnames if that matters). I can apply for my own, it would just be quicker and easier to keep using his.