You can still look up their zKillboard to see their activity.
As for the corporate history stuff unfortunately some weeks ago or such CCP disabled the ESI endpoint because it was overloaded by one of the users and it seems they haven’t re-enabled since then. Kinda odd they don’t keep logs of who uses the endpoint to know who to ban or whose access to disable or something. You should be able to look up that info in-game though.
Although maybe this is another case of them using something as an excuse to justify something they don’t want to openly admit so who knows what the truth of the matter actually is.
Either way as noted in my first paragraph you can still look up the more important data which is their killboard through the link on their EveWho profile.
Edit: Maybe this post has the correct answer, not an expert so no idea but seems reasonable: