Unfortunately, WSPs contain compiled code, not source code. Of course, if the code in question is javascript, then that is easily obtaintable. For c#, there are a variety of tools, such as ILSpy to decompile the code. [Here][1] is a similar question with answers that recommend different tools.

For future reference, both visualstudio.com and github have source code control, and both offer it for free. 


  [1]: https://reverseengineering.stackexchange.com/questions/12874/recover-source-code-for-c-exe