If your case is well ventilated there is no need for that.
GPU itself can stand very high temperature without frying, but heat coming from sink may damage other elements on mainboard, PSU, CPU, capacitors, whatever....
I used to have a Zotac gt210. Yes, it did not have any fan and it served me well, even under load it did not pass 50 Celsius, so you don't need to worry. And you can't replace the heat sink with a fan.
If your case is well ventilated there is no need for that.
GPU itself can stand very high temperature without frying, but heat coming from sink may damage other elements on mainboard, PSU, CPU, capacitors, whatever....