ANSWER:

You’re not sinful since you had done your job.

Stay away from her and keep your distance as she can also be an apostate like him for accepting him as a husband and believing that those who say Allah doesn’t exist can be Muslims! 

Sheikh I told your ans to my cousin who’s husband apostate after their marriage..she told this to her uncle who she said knows quran and hadith ans he said just cz your husband said allah doesn’t exist that doesn’t make him a kafir..and she is believing him. I know your ans is correct..my question is will I be sharing any sin if she still stays with her husband..I did my part..