If you had immediately switched off and given it to an expert, most of your data could have been recovered. When this happens, not many have the self-discipline to not try to recover data themselves, which is when the worst of the damage happens.
I've, over the last year, lost 3 TB of data because of electricity surges and being cut off suddenly (living in S Africa), but waiting to recover the data once the electricity problem is gone.
Yes, i guess i had to, but the thought of waiting the time and the fact that the phone is basically with what i can only film now, that would freeze the process for days for sure...
It is good i found that i had at least my photos backed at google, at least