Though I would never excuse that sort of abuse anyhow, the marriage might at least have been consensual at first. The State never was for anyone.
Personally I favor that there is a written, previously agreed upon law, rather than no law. But it should always start as an actual voluntary agreement and from that basic legal framework we could come up with more advanced agreements within (or without).
If some partys opinion on a given contract changes later on, we would have to weigh the consequenses of exit in court. But then it would never involve inherited compulsion and I would still of course always want to minimize violence.