I need ~3400 miles to requalify for MVP and was sent the buy-up offer which I've never done before. I can get 4000 miles for $625 or 62.5K miles and I think I understand that paying cash is more efficient (i.e I could use those miles for a much more valuable award). Is this correct reasoning?

This is separate from the discussion of whether I should mileage run instead, as there are family health issues that are making that difficult. Along those lines, I have a bonus question about what happens if I cancel an AA flight? I literally booked my first trip with them to try out One World for the first time, and it seems like I get full travel credit for the trip but it's not super clear and I dread calling their customer support line.