How to convert Shape in sigle line

Nj,

The happiest solution would be to (be able to) return to the original stroked paths.

There are some approaches to (more or less) automatic ways, such as those in this thread,

https://community.adobe.com/t5/illustrator-discussions/merge-outlines-to-1-solid-stroke/td-p/12955449

A customized way for this case could be to release the compound path and work with each constituent path as follows, presuming individual lines for the ribs, and then one cut for the outer shape and the centre line, which can be one cut for the combination or one for each:

1) Realease the Compound Path and switch from filled to stroked paths;

2) Select the outermost path that holds all the others and apply Object>Path>Offset Path with a negative offset equalling half the distance to the inner paths (half the width of the outermost shape), then hide the original; optionally cut the offset paths at the top or bottom Anchor Point;

3) Create a straight path between top and bottom Anchor Points of the offset path from 2); optionally join the straight path to either of the cut Anchor Points from 2) to have just one cutting path for outer boundary and centre;

4) Lock the path(s) from 2) and 3);

5) Select each of the inner paths and Object>Path>Offset Path with a positive offset with the same value as in 2) to create offset paths that fit in between the outer boundary and the centre line, then hide the original paths;

6) Cut each of the offset paths from 5 at the ends of the ribs and delete the parts that follow the outer boundary and the centre line;

7) Make sure that each of the ribs ends directly on the outer boundary/centre line, move to snap if needed, Smart Guides being your friends, telling when they are within snapping distance.