This sounds like a bar exam hypothetical. I hope you aren't using Avvo to study for the essay portion of the test, which happens to be tomorrow in MA. (And if you aren't, my apologies, but the question looks starkly bar-exam like.)
There's some things in this question that aren't clear. What's "the settlement" you're talking about, for starters? Obviously, the person who started building the 7-Eleven is in the wrong. Depending on whether the transaction was completed or not, either Bart or Ruby--whoever the rightful owner is--should contact a real estate attorney ASAP. It may end up being necessary to seek a court order to evict the developer and restore the land to its unadulterated state.
Douglas Lloyd is licensed to practice law in the Commonwealth of Massachusetts. Answers provided on Avvo are intended for informational purposes only; they are not intended as legal advice and do not create an attorney-client relationship. The material is presented with the understanding and agreement that I am not engaged in rendering legal or other professional services by posting it.
How to address this really depends on whether you are Bart, Ruby or the 7-Eleven developer. Bart may have recourse to get out of the agreement if he wants to. Both he nad Ruby have recourse against the developer who is in the wrong, and can either be ejected from the property (e.g. removal of the trespassing development), or will require payment of damages to the owner of the property - either Bart or Ruby depending on whether the purchase deal proceeded or not. Each party will need to get an attorney as this is a complex issue with a lot of value at issue from everyone.