If you are excommunicated from a church and you go to another church, Heaven has not accepted it – you are still excommunicated because you have been bound on earth so you’re bound in heaven
Flouting corporate authority is a serious offence in Heaven’s eyes
A person can lose their salvation when excommunicated by the church for flouting corporate authority because Heaven sees them as a publican
To join another church, you should be released not excommunicated
If someone has joined your church without being released, go back to their pastor with them to talk – they’ll either be taken back or released properly