Well, it seems a convenient trope that would handle the three main leads would be to find out that Nagi's somewhat eccentric grandfather turns up one day to explain that Hayate can't get involved with Nagi because Hayate's parents aren't his real parents - but that he was given to them to take care of because of the scandal that would have broken out if it was discovered that Nagi's father and A-tan's mom (or other way around depending on your mood) had an affair and Hayate was the child. So he's actually a blood relative of both Nagi and A-tan, his debt is cancelled by his share of both fortunes, and he's now free to pick one of the other girls to move forward with...
Just trying to see if there are ways to have an ending with most of the leads at least somewhat happy
