Any personality changes after cardiac bypass surgery?

Sometimes. Although many patients experience some effects on the brain as the result of cardiac bypass, personality changes are not particularly common. The most common changes require sophisticated neuropsychological testing to detect. Drugs and unanticipated adverse outcomes can also affect personality following surgery. Off pump surgery has been touted as a solution, however this has not been born out.
Yes. Neurologic changes (including personality changes) are common after cardiac bypass surgery and have stimulated research into off-pump cardiac bypass surgery and types of anesthesia and other maneuvers (hypothermia) during bypass surgery ... Don't forget the effects of pain medications and heart medications related to heart surgery ...
No per se. Some may get depressed if they have significant deterioration in their functional activity due to a severe heart attack, heart failure etc and can't deal with it. Get help if needed hopefully the bypass will give you many more productive years. Good luck.