Why not restore the tenants to a different environment that is not otherwise active? At Atlassian's scale you would expect them 1) not to be running all the things on one server anyway, 2) have some existing ability to move tenants between environments for legal or performance reasons, 3) have the ability to backup/restore single tenants, and so on. I am not arguing that the predicament they are in now is real, for them, now. But I have worked at much smaller outlets where this worked fine, not because they were smaller, but because they had that particular shit in order, which is entirely a matter of priorities.

Nothing, and I mean absolutely nothing, that Atlassian has to offer is rocket surgery-kind of hard... yet, here we are... not being particularly surprised at all.