Both high voltage AC and DC lines are disconnected after the voltage divider, thus the highest voltage present at those pins will be up to 200V.
Yes BSS127H6327XTSA2 is exactly what I use already in this design.
Ok so the op amp circuit is for measuring the high voltage input (VACL to VACN), and you'd like to be able to disconnect this circuit from the high voltage to reduce loading.
You also mention a voltage divider, but I don't think that's shown on the schematic. A voltage divider on the high voltage would also draw phantom power, right?
Also your schematic wouldn't be effective if the input is AC (or, more generally, if either VACN or VACL go negative with respect to your circuit GND), as Q11 and Q14 will only block current in one direction. To work with AC you'd need to replace each with an antiseries pair of FETs (like in a SSR).
Aside from that, yes I agree that 200V between pins of a SOIC is not a good idea (IPC 2221B recommends at least 50mil clearance for 200V).