Is it necessary to replace the brake pad wear sensor when renewing the pads?

If it hasn't made contact with the disc then no but you might find it's gone brittle and just falls to bits when you try to pull it out of the back of the pad. This is what happened to mine so ended up changing it in the end.

For the sake of £15 from Euro car parts I would just buy one in case it breaks, if not you have one for next time. 2017 SVR. SVO Scafell grey Ebony interior
2012 3.0 SDV6 Autobiography santorini black with ebony/cirrus interior. Gone