Question: how to upgrade (actually or functionally) a subgroup into a main group

In the Loomio group Worker Co-operatives, we are discussing migrating the community to another already-existing (Discourse) forum, and using our Loomio account solely for members of its (currently, only) subgroup, Solidfund. I understand that it's not possible to 'promote' a subgroup to become a main group, so how to handle this with minimum disruption if the change is agreed? For instance: just maintain the existing main group as a 'shell' without any members, maintain the Solidfund subgroup as a subgroup, and add additional subgroups if we want to (as we do!) have subgroups of the subgroup? Could/should we remove all the current members of the main group and rename/redescribe it to make the change clear, without disrupting things? At the moment some members of the Solidfund subgroup are only members of that subgroup, while some are also members of the main group.

Hope the question is clear, just looking for peoples' experience and practice. I imagine it's been encountered before.

Thank you!