I don't know if shunning is any worse in IFB churches than in other movements - it's a mixed bag, how IFB churches respond.
Church No. 1 - I left one IFB church after one of their missionaries accused me of heresy for not believing in dispensationalism. The pastors assured me of my support and expressed the wish that I would stay. I withdrew my membership but continued to attend as a welcomed visitor, and after some years the senior pastor invited me to teach in the church Bible institute, which I did.
Church No. 2 - I left an IFB church after being accused of not being loyal enough to the pastor. Not only did they shun me, but they contacted my new pastor to demand that I be removed from their membership. They falsely accused me of being a Satanic infiltrator, and placed a lifetime ban of excommunication on me, which meant that I was not supposed to join a scriptural IFB church again, ever.
Church No. 3 - IFB church, similar to Church No. 2, second verse same as the first, I was accused of not being loyal enough and of plotting to take over and destroy the church. So I left the church rather than continue to take blame as a scapegoat for the ongoing decline of that church, but I expressed willingness to meet with the pastor and anyone else who had a problem with me, to discuss their accusations. The pastor declined to meet with me and the people mostly cut off contact with me. However, they made no attempt to get me in hot water with my new (non-IFB) church.