I think you misunderstood my reply, that isn’t related to corrupted unions. You can union parts with scripts in them and recover the source from those scripts by separating the unions. This also includes server scripts, you can insert a server script, and, when Roblox goes to download the union, you can take the cached union data from the Roblox cache folder and extract that script’s source, which works in published games. This is just a side effect of how unions work, their Child Data is in exact same format as an rbxm file, and this is how Roblox handles the Separate action on Unions.
As for corrupted unions, if you duplicate your union (ctrl+d) and attempt to separate it, but nothing comes up, the data is unfortunately lost. If the union does properly separate, you can just hit the Union button to reunion them. Otherwise, you should try one of the resources like this one: How to recover invisible / corrupt unions