And if you end up with more than one AS due to a merge, you usually pick one them as your primary and connect the other ones to it, then announce their prefixes

And if you end up with more than one AS due to a merge, you usually pick one them as your primary and connect the other ones to it, then announce their prefixes from your primary, ie. your primary AS becomes transit for your other ones. That way you only have to maintain one external border.