Since the wet-wall parallels the joists it does not support the floor above. It is a partition wall and is likely 2x6 to accomodate a large diameter soil stack or HVAC vents. Replacement can be confined to just the area affected by rot. this means you can get away with cutting out the rotted sill plate and cutting off the studs above the point where rot occurs then simply laying in a new sill plate section and either a cripple wall comming up to the cut-off studs or splice into the cut-off studs using short 2x6 and metal splice brackets. Since the wall is not load bearing, you can probably don't even have to worry about bracing it while you cut out the sill plate and subfloor, as long as there is something left to support it. There are limits, if you take out more than about 3-feet you will need to provide some support.