What is the ruling on someone who entered ihram from the Miqat of As-Sa'diya with the intention of 'Umrah, then was compelled to exit ihram and enter Makkah due to being prevented from entering the Haram by car, and he is now in Makkah and wishes to perform 'Umrah? Is anything incumbent upon him? And from where should he enter ihram if he resides in Ash-Shara'i' outside the boundaries of the Haram?

The basic principle is to complete the 'Umrah. If you assume ihram for it from the miqat, you remain in your state of ihram. You must refrain from all prohibitions of ihram until you complete your 'Umrah and exit ihram. You are not required to assume ihram from another place. If you wear a sewn garment, you are liable for a fidyah: fasting for three days, or feeding six poor people, or sacrificing a sheep. As for destructive prohibitions (such as cutting hair and trimming nails), there is one fidyah for each type. For things that fall under indulgence (like wearing sewn clothes and using perfume), there is no penalty if you were ignorant. If intercourse occurs out of ignorance, your 'Umrah is not invalidated according to many scholars.