TAs are expected to take a group. Not just for a lesson, not just for a day but actively teaching all day every day for the foreseeable future.
I don't have a TA. We have one TA who floats around ks2 but doesn't ever seem to make it to UKS2.
Neither do we have the room. Our school has expanded from one form entry to two form entry over the past few years and we have built a new building to accommodate this. But there are no spare rooms at all. 121 support and intervention often happens in the small PPA room or corridors. So no capacity to split whole classes full time..
It's not ideal but talk of abandoning your class or never being able to go to the loo is being a little OTT and not even trying to find solutions.
The problem is that 99% of the time, it might be ok. Like it would probably be ok if you left your 6 year old home alone while you popped out to get a bottle of milk but you still wouldn't do it. But if the worst happened and there was a fight; someone fell and banged their head; stabbed themselves in the eye with a pencil; threw up; scratched someone... I wouldn't be able to justify having left them alone.
On days where I have playground duty and so can't go to the loo at break time, I deal with it by not drinking during the day so the need doesn't arise. I've leaked through to my clothes when I've been on my period and had to wear my coat for the rest of the day, claiming I feel a bit chilly, because there was no chance to go to the loo and it wasn't safe to leave the children.
Grabbing another teacher to keep an eye on them in an emergency is one thing but doesn't work if they're out doing PE or in the library in the other side of school and it's just you. Neither would it work as a long term strategy.
It's not being OTT, it's just reality.