What will happen to apps i bought in a different country after i upgrade my iOS now?
I moved from Germany to the Netherlands four years ago. I have only a single account. Once I got a Dutch credit card, I was enforced by Apple to switch countries for my account. This had the following effects on my account:


I was no longer able to update my iOS apps in iTunes on a Mac. It told me that there are updates, but when I wanted to perform them, it refused to do so. 
I was always (and am still) able to update my apps in the AppStore on my iPad (which I had already in Germany).
I am no longer able to buy stuff on the German AppStore on my iPad.
I can buy stuff on the Dutch AppStore on my iPad.
"Dutch apps" and "German apps" are indistinguishable on my iPad.


I later bought an iPhone in the Netherlands, which was never associated with my account while it was still a German account. Same picture as with the iPad: I can buy only in the Dutch AppStore, but can run my old apps and the new ones. Old apps update from the Dutch AppStore, even if I bought them in the German one.

Both the iPad and the iPhone got updated versions of iOS and the situation stayed the same. 

You should check if the apps you are running are available in your destination. If so, it worked for me.