Best way to remove stripped screw in motherboard

So you've put back in the battery at this point and now just need to fish out the cable which is stuck under the logic board.

Sounds like your driver is not a T3 Torx or is well worn! I would try to get a replacement bit and you might try a T5 bit to see if that works.

Ideally, you really should take the logic board out but these flex cables do have a bit of flex, the only down side is the connector here is quite large and won't roll up and out, unlike the older keyboards which had a ZIF ribbon design unlike this series.

Just the same get a small Allen wrench which you can try to fish out the cable be ever so gentle! You don't want to damage the cable or the connector. See it that saves your bacon. Good Luck!