How Screwed am I?!

I put the boat in the water last night for the first time this year. .... 10 seconds in I noticed a fair amount of water pooling up below the engine. One of the expansion / freeze plugs on the blow (my port side stern plug) was laying at the bottom of the boat.

... I can only imagine this occurred from some water still in the block over winter. I bought a rubber plug to replace the brass one that popped out, so I'll try that, keep on eye on engine temp, oil level, for milkshake oil, and water exiting the block in an obvious crack .... but what are the odds just this plug popped vs. the block itself?!

I'm still racking my brain how it happened... I've winterized my boat(s) for the last 12+ years and no issues ever. Finger crossed it was just this plug vs. the block, but I'm not super confident right now.