There was still immigration and customs enforcement going on before the agency named ICE existed with that name. Regardless of what you want to call it, there will be an agency doing those things after ICE is abolished. There is not a world where the US stops enforcing immigration and customs laws after ICE is gone. The best we can hope for is the current ICE goons get sent to prison and a new organization gets built from the ground up that is less shitty.