unable to open ods file after last edit

I have a large 40 sheet file. Not a huge number of formulas and the few are fairly simple.
The last edit I made included a link to another large spreadsheet to get a total.
There were some other small changes however the link feels like it would be the most significant of the small changes.
I am unable to open this document now. No error message just a grey window when I try and open.
I made a copy of the document, modified the extension to .zip, opened that and opened the content.xml. This basically works even though the content.xml takes a long time to finally format when displayed in InternetExplorer. If I open it in Firefox it is much faster. It seems the default for .xml is to open in a Internet Explorer. I then saved this as a .txt and it opened well enough. Saved the .txt back to .xml.
Tried opening the document again and still appears to be doing nothing but showing an empty window when trying to open. I changed the name of the linked file so it should not be found. Still just hangs with blank screen on opening. Am now leaving it for extended period to see if it will eventually open. Will wait up to 6 hours.
Is there any way in the content.xml to strip away all external references?
Is there any way to separate out separate sheets within the document from within the .xml or by editing some other part of the file content that can be viewed when in a .zip format?
Are there other suggestions for going about resolving this?
I have a backup from December but nothing since then.

I can’t give you an answer, but a description of how to secure your work a little better in the future:

[Preventing data disaster](https://wiki.documentfoundation.org/Videos/Preventing_data_disaster)