I would try to cut and patch and not touch the pillars because what you cant see is the multi-layers in the pillars.
This is a picture of what you will find when you cut the front pillar below the roof line
You would only be able to weld the outer metal frame and not the multi layers inside which make up the structural part of the pilars.
Also it would have to be measured and replaced perfectly or the windshield would not fit.
a few pics...
after replaced roof skin...
multi layers of metal....
sunroof skin out... drill spot welds from top
lead front pillar..
donor roof ... drill spot welds from bottom/inside on this one.
you just remove the skin from donor roof and cut out about 93 spot welds on each roof.
Then install new roof skin.
You will not want to cut the pillars because they are formed by muti-layers of metal.
torch out the factory lead at the 4 seams.