Do you e power guys ever worry about bit flip from a stray cosmic ray or alpha particle disturbing your timer or esc while flying?

A bird strike or broken line is more likely.  With me, a fatal (to the plane) pilot error is more likely!

THANKS now I have something ELSE to obsess about..          

Well, maybe not, most memory has built in error correction for just such a contingency.  I just wondered about the escs and controllers where they are so minimal and stripped down...

Don't have a clue (yet), but I did have a "COSMIC RAY GUN" when I was a kid...........

Don't point that thing at my plane when I'm flying !!!

Seriously, the chances of a "bit flip" problem are small -- microprocessors and other integrated circuits are designed to be generally reliable; if they were susceptible to radiation they wouldn't make it out of the prototype stage, at least at a responsible manufacturer.  This means that even a "stripped down" bit of kit like an ESC or a timer is going to inherit that general reliability from the parts its made of*.  While radiation may be a source of the occasional random error it's not a huge one unless you're flying someplace that's not healthy for you.  I think there's enough people flying electric now that if this were a huge problem with reliability in these things we'd know, and we'd still be flying nitro planes exclusively.

* Assuming that the engineers that design the circuits don't screw things up.  That's always possible, but that's what product testing is for.