The server keeps counting past that. Sometimes when you do AI Battle or some other mode (I forget which one exactly) it'll show you your real coin count when you get your earnings. Last time I saw it, mine was over 12 million.

I broke my bank a while before I even set foot in the Krypt, and after opening everything except the Kytinn Hive (and also spending a couple hundred thousand rerolling gear slots) I still haven't dipped below 9,999,999.