Seems hit or miss with me, but I've been able to open the block editor for the block that lost it, and it STILL has the paramters/actions in there... and I just tweak something and undo it (just to make it think I did something) and then 'save changes' and it brings it all back.
Sometimes, though it loses all paramteres/actions in the block definition even :\
Other times... no idea why... but it re-blocks it. The dynamic block is there there, but it's been made into another block (dyn. block within a blocK) and I hit the ol' asplode button, and the dyn block is there for me to enjoy.
...rarely :\ But sometimes.
Thanks for the tip, though CMDRDUH, I'll keep that in mind... just had this happen the other day, to me.