I've worked in the pizza industry before on and off over the years and I have a similar story where everyone quit...except it was worse and not at a pizza place.

I was working Room Service at a large hotel in a major city one frigid freaking cold Wisconsin January. The pay was horrible and the walk to work was an hour but like you said, sometimes you get into a workplace where the coworkers click and everyone helps everyone to keep chugging along. Obviously I was looking for other jobs and I finally get hired, and I was going to drop my two weeks notice at the end of that week on a Friday.

Wednesday rolls around and I let slip to my Food Service Manager that I got a new job and I'm going to drop off my two weeks later. He tells me that he just got engaged, is moving to Arizona, and plans to basically quit on the spot that day. My Restaurant Manager hears this and not wanting to deal with the literal troll down in HR once our FSM leaves, says he's going to jump ship that day too. This spread to all of our day shift cooks, all of our waiters/waitresses, and our Head Cook (a veteran of the USAF who had a temper and I'm talking Red Lantern type of Rage). Once I hear all of this I figure the pay is crap and everyone is leaving, screw it I'm in too. One by one we all walked down to HR to drop off our uniforms and wave goodbye.

It was the best day ever.

Our Food Service Manager took us all across the road to a bar owned by relatives of Al Capone and bought dinner for everyone...one of the best nights of my life...but probably the worst for that hotel. They're still up and running so I guess stuff worked out, but yeah...I've been in that situation.