Cheapest way to do it would be:
United award (85K): ORD-LON (stop) LON-KTM (destination) KTM-ORD
BA award (4.5K): ORD-BUF
Admittedly, the BA award is only available on March 20 based on current availabilities. That does seem to be close to the day you would want if my arithmetic is correct. If it is, then you should book it now. I believe cancellation for BA Avios on AA domestic is just the $2.50 fee you pay (and you get the miles back).