If the credit card is purely in his name then you are not liable, if he cannot pay it and he has insufficent assets he will do a repayment plan, or go bankrupt.
If he was to die the debt, the credit card company along with any others creditors would be repaid from the value of his assets, the creditors are preferred in this situation and anyone in the Will would have the left overs, if any.
I would worry that he has other debt you still do not know about, with one big debt there are always other's in my experience. If you own any joint assets for example a house, if he does not pay the debt the house could be reposessed or in bankcruptcy sold to pay his creditors, be aware be very aware!