In addition to the excellent answer provided by Monica, you need to assess your technical infrastructure. Should your moderator be able to remove many users and posts? You may need to separate some powers between moderators if this type of activity is anticipated to occur again. Obviously, this could be a one time thing, but your users have now seen it happen.
Over the coming weeks/months/years even, this incident will be referred to whenever a moderator seems agitated. It will likely be in a joking manner: "Oh, Mod is mad! I hope they don't go deleting everything. Hahahaha!". Each time this comes up you (or your team) will have to decide how to react. Currently you aren't punishing (which is good). Consider how this will wear on you over time. It is now that you need to act so that those future interactions can all point to the actions that occurred.
Monica mentions that a post mortem is a good idea. I agree. You can use this to determine what happened, how it happened and develop a plan to prevent it from occurring again. Sharing this information with your users is also important. Companies share these reasons frequently. Some have lots of details, others offer only a high level overview of what happened. Each of them, though, explain what they've done to prevent a similar issue from occurring again.
One thing to consider, as I mentioned in my first paragraph, is to separate some moderator powers. Moderators need the ability to clean up users - spam, trolls, etc - but it could be rate limited (only X users can be deleted in an hour). This would scale based on your community size. Alternatively, deleted users could go into a "deletion queue" that a second moderator needs to approve. For spammers and trolls this should be easy to get a second moderator's opinion. As nice benefit to this is that disagreements should cause your moderators to talk to one another. Instead of working in a silo, they have to get on the same page why a user needs to be removed when a disagreement occurs. This adds a bit of overhead to your moderators. Depending on the size of your community this could be a large hindrance. But, it does provide you with an option to consider (and possibly reject). Why not share that with your community too?
Moderator selection isn't an exact science. It sounds like your current process is to appoint a new moderator. In that case, it probably depends on previous community involvement. How have they reacted to the current situation? Can they explain their views in a clear manner? Are they community oriented? They may not agree with you on all points, but do they come across as someone who has the interests of the community in mind and are they able to work with your existing team?