the consequences of overstaying in China for 8 years

According the exit and entry laws of China, you may be imposed with a fine of RMB 500 per day with a total amount of no more than RMB 10000. If you are not able to pay the fine, it is probable that you be detained for more than five days but less than 15 days. I guess you will be repatriated since your case is serious.