Well well... I ended up making my cities again as I lost some saves thanks to a very nice Windows bug appearing after a required update...
Not a problem as I was able to recreate my cities and make them a little bit better, a little bit more efficient !
So I rebuilt Perwadjyt, with one more bazaar to provide everyone with potteries.
And then, the city is supposed to hold on for more than 3 years with no destruction, no loss of inhabitants, just as I wanted !
I did the same changes for Nekhen (1 more bazaar and everyone gets pottery and beer more efficiently).