I am currently in a fairly extensive exploration expedition and get to sell my bio data whenever I get within 1000 ly of a carier. (1000 is the magic number for me)
This time I had for 4 billions worth (incl bonus). I haven't sold any cartographic data yet as I'm saving it for someone who mayne can use it for bgs when I get back
It turns out that fdev will usually restore any lost data in this case but only once.
I did die at the start of the expedition and lost data worth 2 bil. I was devastated and very happy when fdev informed me that they could restore the lost data.
Now I realise that i could have lost way more and that it was not that much of a loss really.