For now if a frr process restarts there is no way to restore it's configuration to the previous state.
This is possible to short-term fix by creating a post-commit script that saves the frr configuration to file after a change in frr.
Also on frr process reload it needs to rewind the config into a running starte on process startup.
All places where frr is changed need to be identified to allow saving of config on eg. dhcp static route change.
This is not supposed to be a long-term fix, because it can cause config inconsistency and a better solution is to rewrite all frr setup script to allow for a vyos->frr sync check. (but that will take much more time to implement)
For now the process is not started, feel free to comment and if your'e want a mission, just assign yourself the case.