One thing's for sure, with all that reinforcing in there it's never going to fall apart.
Just out of curiosity, have you ever had a thermometer in there to see how hot it actually gets?
Without reo, the concrete will definitely crack and break up in time.
I once built an incinerator to burn household rubbish.
It lasted 12 months before it totally fell apart.
I now use a 44 gallon steel drum.
I have taken temperatures inside the Pizza Oven.
900deg C when fully heated.
The door thermometer was reading over 700. C
But I don't cook at those temperatures.
That is only to preheat the Oven.
All the coals are dragged out and the Oven is left to equalise.
Cooking can start at 450deg C.
A Big Pizza only takes two minutes too cook.
At that temperature I can cook 20 Pizzas.
Then all the Breads are Baked in there for the next day.