I am a TA, and I have been asked to take the class.
I am not actually a HLTA, but I do have at least 13 yrs of experience working in a class. TBH I would prefer to "stand" up and work as Class Teacher, than to get a supply in! (plus I have all the plans that the Teacher would be delivering to the children!) The simple reason being is, that I know the children well, a supply teacher doesn't! Quite often its more stressful for the TA with a supply teacher and 9 times out of 10 you basically do the work of the class teacher anyway - so why not get paid for it!
I am very fortunate, the school I work in pay their TA's double time for taking the class! Obviously not every school do that!