No, AFAIK it will just clean up the migration to be able to start over.
To restore the NS7 applications (removing the white screens & enable the services) you can follow the “Post-migration step back” in the nethserver-ns8-migration — NethServer 7 documentation
Good question, it seems that just the SOGo migration didn’t work. It’s easily possible to restore the NS7 so you can check what happened on the NS8 and start over another time.
Some ideas:
Did you try to reboot the NS8 or to restart SOGo as there’s an older thread about the same error which was solved by reboot: Guacamole unexpected internal error - mysqld stopped - #4 by mrmarkuz
Do you use SOGo just for mail? If this is the case you may just remove the not working SOGo and start over a fresh SOGo install. When mails and user domain are migrated correctly it should just work.
AFAIK SOGo has an export/import tool, maybe it can be used to transfer calendar/contacts to the NS8…