Not that complicated. Neighborhoods change. Has very little to do with Jewish people, in particular. People with the means don't want to live in a poor, high crime, high blight neighborhood like the Bronx after WWII. This is true for people of all religions. I don't think there are many Anglo Catholics left up there either. Similarly, the neighborhood my dad grew up in had a large Jewish population (for Memphis) in in the 1950s. Today, it's not an area one wants to spend a lot of time in. I don't buy the whole highway thing. There are plenty of very nice neighborhoods near highways. Including, as it happens, the current Jewish part of town in Memphis.
The highway thing was more about its impact on cutting up neighborhoods and displacing residents than simply being near a highway. The people came first, than the highway which cut through neighborhoods.
As far as where they went, as has been mentioned you do have a sizeable Jewish population in the Riverdale section, . I would say the highest concentration went to the northern suburbs, but it was a bit all over the place. Some went north, others went into Jersey, some into other parts of the city, some to LI, others down to Florida.
