Same here. Just got the Marshmallow update last night, and got locked out. Rather than fingerprint, I was using the pattern to unlock ... the phone now doesn't recognize my pattern nor the backup password, nor the option to log in with my Google account.
After 3 frustrating hours on the phone, between Sprint, Samsung, and Android, I got the apology "I'm sorry but you'll have to reset your phone, which may not actually solve the problem because you may still be locked out ..."
People here seem to have had success waiting awhile for the option to appear to log in with Google ...