Is the marriage considered void if the wife embraced Islam first and was forsaken by her husband, then the husband embraced Islam later and she returned to him, and is it necessary to renew the marriage contract in this case?

The statement that the conversion to Islam of one spouse annuls the marriage is incorrect. The spouses remain in their original marriage if the other spouse converts to Islam before the expiry of the iddah (waiting period). If the other spouse converts to Islam after the expiry of the iddah, they can return to each other with the same original contract, without the need for renewal, unless the woman has married someone else. This is the chosen opinion of Sheikh al-Islam Ibn Taymiyyah, Ibn al-Qayyim, and Sheikh Ibn ‘Uthaymeen, who based their argument on the story of the Prophet, peace and blessings be upon him, returning his daughter Zaynab to her husband Abu al-‘As with her original marriage, after he embraced Islam two years later and her iddah had most likely expired.