Thanks, I will start the import soon.
FTired wrote
"What will happen to posts which are not in that archive, i.e new posts will they still be there, or get deleted"
They won't be touched. So - at the end of import - the forum will have both old and new posts together.
FTired wrote
also "What about posts which are in the archive AND currently in the link above, what happens to them, do they just get replaced"
They will be skiped by the importing process (as long as they have the same Message-ID header, which is probably the case).