TOGA is not required by OPS regulations (not talking about certification), the same way that it is not required to reduce weight if you can make it with TOGA even if you are not a test pilot. You even take advantage of the actual temperature compared to the assumed one. If you're using a derated take off procedure you cannot recover the max TO power and you aren't unsafe.
Consider TOGA? Yes, of course!
How is the aircraft climbing? Are there obstacles? Was the take off limited by climb gradient or Runway length? Do you need to over-stress the single engine? What was the reason for the dead engine to fail? How is doing the good engine?
Maybe you've hit a flock of birds. That's why you have an engine failure and you don't know how is affected the live engine.
Maybe...a lot of possible situations.
From my point of view, to teach "Select TOGA as per procedure" is not correct. You have to teach that it is not mandatory, because it's not.
In the other hand, TOGA has always to be considered, so "Consider TOGA" IMHO is the right way of thinking...and teaching.
It's just my opinion, nothing else.
. And it's legal of course.