Not wanting to go to your husband's friends' gathering is perfectly understandable. You may not want to hang out with people you barely know; you may just not feel like it, or you may be out of money to go to that. Whatever the case is, you are fully entitled to say no; you were invited, not obliged to attend. Not allowing your husband to go just because you don't go is different; that definitely is wrong. The thing is, you can say no to as many gatherings as you want; you can even dislike your spouse's friends; that is also acceptable; we don't like everybody. So, if you are like this wife and don't want to attend what your husband's friends are planning, don't go!
You don't have to come up with an elaborate plan to reject the invitation to attend somewhere. You can just say "thank you for the invite, but I can't", and that should be reason enough. If it is a close friend, they may be entitled to demand a better explanation, but you can just say white lie and go on if you don't want to get into details. Even if we really want someone to come to our gathering or party, we have to accept that they may not want to come. We are just inviting them; it can go one of two ways: they say yes or deny the invite; in either case, we need to accept it. If it's a very close friendship, them not coming can break the relationship, but that is something else. The important thing about all this is that we can't be obliging people to come to our things. We just have to accept what they say to our request. So, even in this case, if the wife doesn't want to attend the friend's things, she will always be able to say so, and they have to accept it. The husband also has to accept it. And of course, he should be able to attend on his own; it may not be the same, but as she is entitled to reject the invitation, he is entitled to accept it.