This is such a poor reading of landlord/tenant law that it is actually absurd. Please tell me you don't rent properties, because if so you need to brush up on landlord/tenant law.
And before you say I'm some bleeding heart landlord hater, I'm saying this as someone who works in the real estate industry and property management. I actually contacted my Congressperson asking them to vote to end the eviction moratorium.
For starters, all tenants have a legal right to quiet enjoyment of their homes. When you rent a residential property anywhere in America, the law says you are "buying," among other things, the right not to be harassed by other people. This includes harassment by your landlord, your neighbors, and potentially even your roommates. If OP had told the landlord before choosing to leave, then yes, the landlord would be legally obligated to remedy this.
Because the two roommates harassed OP based on her race, those two roommates likely violated the Federal Fair Housing Act. Harassment from a neighbor or roommate that interferes with your quiet enjoyment of your home is a Federal Fair Housing violation if it is racially motivated. Harassment by neighbors and roommates is one of the most common Fair Housing complaints. To be clear, it's the two roommates that are potentially guilty of this, not the landlord.
Now all this being said, because OP is leaving, there is nothing the landlord is legally obligated to do at this time.
It's no different than if OP was moving out and let the landlord know that the heat was out as she left the property vacant, or if she informed him that the two roommates were hoarders making the property unlivable. The landlord doesn't have to make it right for OP or compensate her, since she didn't tell him until she left. But the landlord absolutely has an obligation to make sure it isn't an issue for the next incoming tenant.
Regardless of whether or not OP tells the landlord, the landlord is legally obligated to take reasonable actions to remedy this issue as soon as the next tenant mentions it.
All this really comes down to is whether you would rather the landlord have days to fix the issue, or months to fix the issue?
If OP tells the landlord now, then the landlord will have weeks if not months to figure out what, if anything, he is going to do before the new tenant moves in. This helps both the landlord and the incoming tenant. Maybe he just closely monitors the situation with the new tenant. Maybe he gives these two assholes a stern talking to. Maybe he doesn't renew their lease, and can spend the next few weeks or months of their remaining lease screening new tenants so he doesn't miss a month of income. And if push comes to shove, the landlord now has a paper record to help establish this as a pattern to justify evicting these two racist clowns.
If OP doesn't tell the landlord now, then the landlord will be blindsided by this if the new tenant complains about experiencing the same problems. This helps absolutely nobody except the racists. He won't have weeks or months to figure out what to do, he will have days. He won't have time to screen new tenants to replace them, meaning he will lose income if he needs to kick them out. Even worse, maybe the landlord doesn't believe them because to his knowledge, they never caused problems for OP. And, at that point, if the landlord doesn't act, then the landlord is violating with the new tenant by failing to protect his tenant's right to quiet enjoyment of their rental. And now, because he is only finding out about now, the landlord will have to resolve the issue in a much shorter time frame.
OP would be doing the landlord (and the incoming tenant) a favor by making the issue known weeks or months in advance of it becoming an urgent issue that needs fixing immediately.**