Hmm... on my system, the Spark icon is always inside the little popup menu that you have to click the Up Arrow to see (in your screenshot). Does the icon move into that popup menu after explorer relaunches (I know, a basic question, but want to make sure we cover all bases).
Also, are you seeing this behavior when you forcefully crash explorer via Task Manager as well as normal explorer crashes? I have only been testing with focing explorer to end by End Process Tree.
This appears to be the main class that handles the tray icon in windows (there's another for linux)
When I get home tonight, I'll see if I can play with some sort of "check" mechanism that verifys the icon is present in the system tray.