When creating a multi-response/dichotomous the 'base' variables are all kept in the file. So no variables are lost.

There is something to make clear:

+ in Editor Mode, variables will appear in 'grey' color which also visually helps to identify them as variable used to create a new multi-resp variable.

+ in Designer Mode, all the variables that are 'grey' in Editor Mode are simply not displayed, default settings of Datadynamic since Designer Mode is conceived as an instrument to Design Tables.

It is possible to transform that 'grey' variables into 'black' ones which in Designer Mode will translate from invisible to visible.
To do this refer to hiding/showing variables solution.