A way that I've found (and used many times) is to use script variables. I creat a scipt var outside the launch lock, then I just set the var to a specific value at the end of the launch block, which I also check for outside the launch block. Here's an example
The "for" loop should be "warped" to allow reliable "done" semaphore handling but it will destroy the expected visual effect: Snap! 7.0.2 - Build Your Own Blocks
No,
"do in parallel" does not yield and all actions are started at once.
Every "360 deg..." starts at the same angle and draws over the shorter lines.
With, non-warped, "for" loop, actions are started successive one by one with a slight delay, forming the fan blade shape.