Actually pimps had a heavy presence on Backpage, and used to set up ads for many girls. There certainly were independent women on BP but a large portion were working for dudes.
The girls who aren't tech savvy will end up turning to pimps even more now. I'd expect a lot of independent girls to struggle now; sure they have their regulars' cell numbers saved, but they're prob gonna fuck up trying to contact those dudes too much, come off desperate, get blocked, etc. Not being able to juggle those things will lead to many turning to pimps, who will handle that shit for them.
The savvier girls will end up on tumblr/twitter, and some will end up on Seeking Arrangement. Most will probably try to migrate to dating apps.