What are the consequences for one who had intercourse with his wife after passing the Miqat while in a state of Ihram for his individual Hajj, and did not slaughter the obligatory sacrificial animal due to his Ihram? And is it permissible for him to perform Umrah before slaughtering the sacrificial animal?

You are required to offer the Hady (sacrificial animal) that became incumbent due to crossing the Miqat during your Hajj. This obligation remains upon you, and it is permissible to offer it at any time. It has no connection to sexual intercourse or to another 'Umrah. The minimum for this Hady is a sheep to be slaughtered within the Haram and distributed among its poor. You may appoint someone to perform this on your behalf. If you are unable to do so, then fast for ten days, by analogy with the Hady for Tamattu' Hajj.