Modern bias circuit with balance or individual trimmers?

[SoulFetish]

It's very easy to put a safety resistor between the wiper and top side of the pot.

But, I've never replaced a failed Fender bias pot. Have you?

I have on a few occasions, but it's a very rare point of failure in a Fender amp.
Having said that, it hasn't discouraged me from routing bias voltages through wiper in any of my own designs. But, I like redundancy, so I like your suggestion of a safety resistor from wiper to outer lug.