If your south bridge chipset gets too hot then you need to RMA your board or get better airflow... or just a new board because South Bridge and north bridge heatsinks are designed to keep the chipsets at a safe temp... sometimes they do a poor job at it though. If that still doesn't answer your question. Please elaborate it a little more and Ill try to answer
and if your southbridge chipset gets too hot couldt that cause fps loss in games?
You'll have to consult your motherboard manual to figure out which sensors those are referring to.
Heat does not naturally cause performance loss. If a component gets too hot for too long it could fail and as such many components will monitor their own temperatures and reduce performance automatically if the thermals aren't managed properly. If the thermals do not get back in line they will shut the PC off to prevent damage. This is known as "throttling".
The Southbridge handles secondary storage and IO. The SATA/PATA/SAS/SCSI/FDD connectors all terminate here. Add-in storage controllers connect to the southbridge via PCIe lanes or other peripheral connection methods. The Real Time Clock, firmware EEPROMs, USB root controllers, RS232, LPT, PCI, ISA and sometimes even Ethernet terminate here as well.
The southbridge is a chip that primarly services peripherals and in some cases provides enough PCIe lanes for a third or fourth graphics card. Attaching a graphics card to the Southbridge has never worked well as it requires another bus hop to get to the main memory which is attached to the Northbridge.
On Intel platforms the Northbridge has been completely integrated into the CPU. AMD has integrated the memory controller onto the CPU but still relies on an external Northbridge for the IGP (on non APUs) and PCIe lanes