It would play out a little different for me I suppose....
If I woke up and I sucked at photography, that would certainly mean I was no longer able to make a full time living off of it.
So the first thing I would do is sell everything and take that money and get a science degree with an emphasis on applying it to renewable energy technology, which ironically, is currently a hobby. I could not do photography as just a hobby because I would no longer have the time to dedicate to it that I have now and the creative freedom that provides me, it would be too hard to lose that and just have to "settle".
So if my hobby of solar became my job and I left photography behind, I think I would engage in playing more guitar...as my hobby.