Eboard member (M20) abruptly resigned. Me (F20) Vice president extremely baffled at what to do next

Hello! Sorry this is a college/school drama instead of the juicy relationship stuff, but I'm in need of some help.

I'm in a cultural/social club in college and it is pretty serious. I'm talking about events nearly every week, and our big spring event usually has hundreds attendees. Needless to say, there is a lot of work that goes into these events, and this club is pretty time consuming.

One of the board members, let's call him Daniel, has a position on board where he is in charge of one of our biggest fall events. There are typically two people in this position.

Yesterday, Daniel messaged the president asking if he could miss our next event on Thursday because it was his fraternity's bid night. We ended up deciding to ask him for his fraternity president's contact information just to talk to them and figure out how to work out future event conflicts.

We never heard back from him until later that night when Daniel messaged the eboard GroupMe (it's basically easy group texting) and wrote a message to all of board that he is stepping down from his position. He did this without telling internal board (President, VP, treasurer) which I find disrespectful and unprofessional. Second, he abandoned his co-chair and basically left her to carry both their weights in planning the fall semester event.

His reasons are that he can't handle the workload anymore. I don't know what other organizations he's in, except for his business fraternity, which understandably takes up a lot of time. However, the big work load is honestly what he signed up for when he ran for the position. He knew how much time he'd have to put in because it was emphasized it a lot during his election. In addition, I'm good friends with one of his pledge brothers and she mentioned that there's a big name business club that meets at the same time as my club, and she hinted that he would have a lot of incentive to go as a Junior year business major. I'm skeptical whether to take her word head on, since it didn't come directly from him. Regardless of his reasons, which can be understandable as sleep-deprived college students, the WAY he resigned put a bitter taste in my mouth. I think a good way to put it is do what you gotta do, but do it the right way.

What I need to know is:

How does the eboard as a whole react to this? I think our #1 goal is to remain professional, and I don't know where to go after that. I just know that I would be livid if he put us down on his resume. This may be vindictive and petty, but I feel like no one should get away with this kind of stuff. It's only gonna hurt him in the future if he can't act professionally.

I also want to know, how do I address this event with the rest of eboard? They already know that he resigned, but we still gotta say a few words. Our goal for this is to set an example of Daniel because I don't want any more eboard members leaving. I think our org would fall apart at a remarkable rate of 2 weeks of school.

TL;DR: eboard member upped and went in an extremely unprofessional manner. How do we handle this?

Thank you in advance.