Hey Martin,
1) Do you store activation details within this file?
No the activation details are stored separately.
2) If you re-deploy this file to a production user who has already activated and the file is overwritten - what happens? Do they lose they're activation details and need to re-activate?
Nope.
3) what is the purpose of the file if you don't store activation details inside it?
It contains things like your product name, company name, infromation needed to verify product keys, etc.
Tell me if this helps.