Is it obligatory to repeat the Hajj for someone who was unable to offer the sacrificial animal (hady) during Hajj, and thus owes ten days of fasting, and wishes to fast them during ‘Umrah?

If you performed Hajj as a "mutamatti'" (performing 'Umrah then Hajj), you are obligated to slaughter the sacrificial animal (hady) in Makkah during the days of Nahr (slaughtering). If you cannot slaughter it yourself, you may appoint a trustworthy person or institution to do so on your behalf. If you delay the slaughter until the days of Nahr have passed, you are still obligated to slaughter it. As for one who cannot find a sacrificial animal, they must fast three days during Hajj and seven days upon returning to their family. Your Hajj is valid.