Can the U2 IC chip be reballed / flowed with heat?

That depends on what the root problem is.

If the U2 chip is defective, no amount of reflowing or reballing is going to solve the problem. Considering that a replacement IC is relatively inexpensive, the best option is to replace it. That way, if the problem had to do with faulty connections or oxidized "balls" or pads, this can be fixed while replacing the IC.

That said, this is not a trivial repair by any means. This IC is small, just a few millimeters per side and has 42 balls in that tiny surface. If you don't have the proper tools or experience, it can quickly become a quagmire.

IMHO, you should consult with a qualified repair shop that does micro soldering for a proper diagnostic.