Just wanted to record this for those who may encounter this problem.
I had been printing for about 3 months with a batch one taz when the extruder stopped heating yet the thermistor read correctly. The likely source of the problem was diagnosed with a helpful Claudio from Lulzbot support over the phone using a multimeter.
Definitely consider keeping a few extra heat resistors on hand as this problem will surely occur at the worst time possible, as it did for me.
3 months of regular printing seems short, but I’m new to 3d printing and this could be normal.
An aside, I ordered the replacement part on a Friday AM with expre$$ shipping from Lulzbot and didn’t receive until Wednesday afternoon, not quick enough for me.