Bathrooms had an immediate utility for people and quickly found use as bathrooms quite often. All that changed was they took down signage. Sometimes they became "employee" bathrooms because they weren't as nice as the formerly white only facilities. Sometimes they were shut down as redundant or found another use as utility closets, at least in commercial buildings. Public, or civically funded bathrooms fared similarly to other public accommodations such as parks and pools.

Other facilities such as public pools didn't fair so well. De facto segregation quickly replaced de jour segregation and as black people entered these public spaces, whites quickly fled. In Jackson Mississippi in 1962 for example, the mayor ordered all public pools and bathrooms closed after losing a court case. They went so far as to remove benches and picnic tables. Livingston Park had a gorgeous lake built during the New Deal that was a public swimming and boating facility. That was quickly shut down and never reopened.

In the first half of the 20th Century, large public swimming facilities were a hugely popular attraction, but were whites only. Much of the "local level" fights over desegregation were to gain access to these honestly gorgeous facilities with slides, diving platforms, and fountains lasted well into the 1970's. Cities largely had neglected to provide similar facilities to black people even after previous SCOTUS decisions required that separate but equal meant similar but separate facilities had to be provided. Black people just didn't have access to swimming pools (which is pafrtially why to this day, whites are twice as likely to know how to swim than blacks).

In fact, even access to beaches was restricted which played a major role in the 1919 Chicago race riot.

Sadly, because local governments often decided that if they had to share public facilities like bathrooms and pools with black people no one got to have them.