Hi,
on a PCB and inside of an enclosure i don´t think there is a problem.
But as soon as wires go outside and they may be touched, either by human, animals or any other thing you have to protect the circuit.
For a hobby project you can do anything, but for professional use i´d call this a must.
Even the brush of a vacuum cleaner may be statically charged to very high voltage. If it touches the wire then the overvoltage goes to the FET. Even if the other side (drain) is not connected to earth potential there will be capacitive current. This may not destroy the FET at once, but it will hurt the FET inside isolation barrier. Maybe all is fine for years... then maybe the leakage current increases and soon the FET destryos itself.
Klaus