No, surgery is not the only option. It is one of the options for wisdom tooth removal only when it is covered with bone or it is impacted.
Otherwise if the decay is superficial, it can be filled with restorative material. If the decay is deep , then we can go for RCTs.
And if nothing can actually save the tooth or its causing discomfort , then it is advisable to extract or remove the wisdom tooth.
Next Steps
Ask your dentist , take appointment , sit and understand properly.
Health Tips
The nerve involvement will be the only risk factor in major cases.
otherwise it's a normal routine procedure.