There weren't two reasonable parties involved or else there never would've been a house built on land someone else owns. That is not a reasonable mistake. Unless millions of dollars of investment is pocket change, in which case losing that entire investment is also nothing for the offending party. Given that millions of dollars is substantial for the offending party then they weren't acting anywhere close to reasonable.
I don't feel there is a shred of responsibility for the offended party to try and make reasonable accommodations for another party acting so unreasonable.
I don't feel any sympathy for the developer either: I feel bad for the trees that had to be cut down, the materials that had to be mined and processed, the heavy machinery that had to be moved to that location and burn gallons of fuel, the workers that had to spend their time building it all. All that will be destroyed, some valuable materials will be recycled but the bulk will be dumped in a landfill somewhere. Just the waste of it all. And just because some developer, the city, and many other parties along the way couldn't exercise due diligence. And at the end, there was so much spite between the party that no one could come to an agreement that allowed this building to stand.
I don't feel there is a shred of responsibility for the offended party to try and make reasonable accommodations for another party acting so unreasonable.