Datasource switched after publication

Hello, hope someone can solve my issue.

I use power BI desktop with my data model which i publish regularly on webapp with Company premium account. 

I have 3 independant sources (Excel files) for my tables and 2 other Global tables where i have all my DAX formulas for query.

Last publication did end with an error and i've seen all my data sources disappeared from my desktop application.

On web app the message was shown as "incorrect format error"

Now i'm kinda stuck because i'm not able to get the file from the server as it is too big and my local file is empty with datasource but report part. 

I did unfortunately saved after the publication without noticing the issue (I was late for work trip :/) 

I try to change from Web app the data gateway to my laptop to resolve this but nothing is working ... 

My last save is 4 month old and i've made a lot of changes since this date which i naturally did not documented ...

Is there any way to get my formulas back by transfer starting from an older PBIX ? 

This is a huge work very important to me so any help will be greatly appreciated. 

Thanks