Temperature and flash corruption in microcontrollers
A rough back of the envelope calculation indicates that a device with a minimum 20 year retention at 110’C would last about 1/256 of that time at 190’C so you’d be knocking off a year or two from the life. 200’C is a wash with the halving for 10’C approximation so I would pick the lower temperature I think. An hour at 190’C is much worse than a few seconds at reflow temperature when it comes to retention. At 230’C, 30 seconds is the equivalent of only 4 minutes at 190’C.  

Of course my estimate using that rule of thumb may be completely worthless— perhaps you could procure a sample of the MCU chip, program it, bake it for (say) 10 and then 20 hours and see if it loses bits. 

Or find some way to selectively cool the MCU chip.