I'd leave the bolt put and use a second nut.
Trying to remove it will be a huge effort, only worth it if your
insurance company complains or you can not sleep due to worrying.
How did the stripping occur?
How does the overall bolt pattern look like? Which bolt is it? Front or trailing edge, or side of keel?
One reason is that
keel bolts have usually a fairly big amount of
safety in their design calculations, further the bolt does not show signs of
corrosion.
The bolt has been stripped to the bottom of the thread which is equal to its solid diameter at its thinnest location anyway.
One thing I wonder more about is what looks like a hairline crack in the glass beside the bolt (about one bolt diameter away). Might be the picture though...
This is just my thoughts looking at it and not a legally binding professional
advice. :-)
The decision is up to you!