This is not a pastoral advice question, I'm happily married. I just really don't know the answer to this question to help a friend, so I guess it's pastoral pastoral advice, but I definitely don't want a 'try to work it out' answer, just the facts please.
Sacramental marriage cannot be undone by civil divorce, that much is clear from scripture and Church teaching. However, what does civil divorce mean for the sacramental marriage?
If it is OK, what factors should a person take into account when forming their consciences to up and leave (for instance there could be a case where the laws in a particular region require someone to serve divorce papers in order leave their spouse with their kids and not be accused of kidnapping them) and if it is not OK then what recourse does one have to protect themselves and their children against their spouse, that does not constitute a grave sin?