I don't think there's a way to do this without casting something to connect the pre-fab to the surrounding concrete sidewalk. Like how do you precisely cut out the existing curb so the prefab just fits (including elevation/slope) without excessive gaps or something? And if you're pouring concrete anyway, might as well pour the curb itself.

With prefabs you first dig up both road and sidewalk, set up pre-cut granite curbs (kerbs?) on a mild concrete foundation (negates sinking completely), then repour and repave sidewalk and road. Lasts many years in -20C winters +35C summers climate.