There is little to lose, so I'd give it a go Spent ages too fixing it up but suspect it's not just the vreg chip delamination but other components and the multi-layered PCB itself, which has developed small stress freactures over time. Funnily enough I've come across a few non-Apple laptops with similar issues lately (when you flex the board, it boots).

My soldering did result in a 100% working iBook - for 30 minutes. Then 15, then 10. Repeat next day for same result.