It's unlikely that Taiwan will ever give TSMC permission to run leading edge fabs in the US, as that is contrary to their national security (as they perceive it to be).
So owning 49% of a JV, along with their existing customers, makes sense as a way to produce leading node in the US. It may be the only way they can achieve that.
TD would be greatly reduced, unless the former Intel US fabs were also not permitted to get their technology from TSMCs existing R&D group.
They have also made it clear they only want the EUV fabs, so something would almost certainly happen to the older fabs. Maybe Intel retains them, then eventually sells them.
Another wrinkle out of the latest rumors is that Intel board is apparently not keen on selling Products or Design capabilities, but that may be part of the strategic disagreement going on at the executive level.
Wouldn't be surprised to see Apple get involved as well.