Skepticism or Wonderment

I was thinking about a type of person. The person that accepts God into their heart but latter never thinks of him and goes crazy joining to festivities life has to offer. Are they still Christians? Were they ever really a Christian? Obviously it's not in my power to say or know but it makes me wonder. I've had some awesome conversations with people that accept Christ but I haven't seen some of them in years. Is that my fault or was that really how God planed it? Some people can seem to have it all together with what they say but we can never know their hearts.