My sympathy for your loss. Some of this discussion may seem cold, but that's not anyone's intent.
Continuing to use your late husband's miles is the easiest way to go - for now. The problems will show up when there aren't enough miles left in his account for an award that you want, but there are enough in total in your two accounts. At that point you'll want to transfer his remaining balance into your account. To do that, you'll have to provide evidence of his death. That evidence will include the date. AA is likely to notice that someone used miles from that account after the account holder had passed away. If you're lucky, all they'll do is take away his remaining miles. If someone at AA is in a nasty mood, they may try to get you to pay for award flights that he couldn't possibly have booked. If you can plan your awards well enough to use up all but a few miles you don't have to worry about this, but if you might want to merge the remaining 40,000 miles in his account with some of yours for that business class trip to Australia, you do. That's the practical reason why you should contact AA, even if you don't give a hoot about their official terms and conditions or anything else.