It takes a lot of humility for a previous friend to contact you once they have shunned you.
From my experience so far, friends previously shunning me who have decided to make contact were nervous about how I would react - almost expecting me to give them the cold shoulder.
However all our previous friends who are still in, are trapped in a mental prison. If they contact us, they've escaped somehow and need help in adjusting to 'normal' life. If they are still somewhat mentally trapped, i.e. still believe it's the 'truth', then they need treating with kid gloves - it takes time to come to a realisation that they've been sold a bundle of lies.
2/3 of friends who have been in touch realise they've been in a cult only after a considerable amount of reasoning and time. Why should this situation be any different?
And, another thing - if they openly want to be your friend on facebook having shunned you because they view you as a 'dangerous apostate' - something radical has happened in their life.