important question about S4

i know that when you root your phone you can buy a 64GB SD card and then make your phone think that its the internal memory so it runs so fast and you can download whatever games and apps you want.

and i know that SD cards can sometimes stop working for no reason because i had a 32GB SD card (in my S4) and it worked fine for 3 month and then it just stopped working and without dropbox i would've lost all my pictures and videos.

so i wanted to root my phone and do the swap internal to external to my phone but i am wondering what will happen to my phone if i removed the SD card or the SD card stopped working? (when i say stopped working i really mean it, the SD card just becomes a useless piece of plastic and metal :\ )