They don’t. Anybody that does this is marked for life by every side - Apple as well as Oppo, as an unreliable, non-trustworthy personality. If Oppo promised him some position in their company it will be provided as a dunce seat just long enough for other potential IP thieves to think “Hey, this guy seems to have it figured out, I should steal secrets for Oppo!”, and after that reasonabke time period he’ll be buried in some godforsaken back room until he quits.

Traitors are marked wherever they go.