Are the intrusive thoughts that present images of people upon mentioning God and arouse fear of polytheism, despite seeking refuge [in God] and shunning them, considered evidence of the heart's involvement in polytheism, and does that expel a person from faith?

All that you complain of stems from the effects of waswasah (whisperings/obsessive thoughts), and it does not involve shirk (associating partners with Allah) or acting upon the whispers of the self. The cure for this is to strive against the self in ridding oneself of the waswasah by ignoring it, not paying attention to it, seeking refuge in Allah from it, and asking Allah for well-being.