> 1) It may be possible to do this with reflog. I don't know for sure because I haven't needed to do this yet. (I think the main problem is that by default reflog purges old history at some point)

I've done this when I was submitting patches to a large git based project (perl5). The trick is to to the rebase and then re-tag your old branch. That way the old work is there if you need to reference it. Since it has a real live tag, it will not get garbage collected.