I've always thought Bosh was quite overrated, so it's kind of Schaudenfreudistic to see him struggle this way.
That said, I don't expect his rebounding, which should be fairly independent of offensive usage, to stay at an all-time career low for him. I also expect his shooting percentage to at least match his career level if not exceed it by a little bit once he's more comfortable off the ball more and Wade/Lebron get used to feeding others mroe. I'd also expect his minutes to bump up to about 34 mpg.
So, about 20+ games into the season, barring injury to him or Wade/Lebron, I imagine he'll settle into this:
34 mpg, .495 fg%, 16.0pts, 2.0 assts, 8.9 rbs, .9 blocks, .8 steals.
I'll try to remember to check back ~20 games in; it'll be interesting to see where he's at.