If you edit the initial profile used for creating a sheet metal part, the information about the flange is lost too, i.e. offset values and references for subsequent flanges. This can make it impossible to fix a design without starting over which also can break other components in a design:
Of course the reference is lost, if the referenced geometry is deleted. My point is, that when you then associate another line instead, it should remember the settings used for the prior, i.e., lenghts /offsets, so that the geometries depending on the second flange are not destroyed.
For more details see original post in support forum, where there is an additional screencast too.
https://forums.autodesk.com/t5/fusion-360-support/sheet-metal-flanges-and-hence-all-subsequent-featu...
