so sorry to hear about your fig tree.

Fig trees are susceptible to ‘cotton root rot’ which is a fungus that causes quick death. One symptom that is distractive of the disease is the leaves hang on after they turn brown. If this brown leaf effect is not happening, then it may ne crown gall. Read the descriptions at this web site:

https://plantdiseasehandbook.tamu.edu/food-crops/fruit-crops/fig/

The other problems are:

Application of weed and feed fertilizer applied on the lawn and the product run off lawn into to the fig tree area with either irrigation water or rainwater. Also some fig tree roots may be in Lawn area

Digging near or across the roots to bury cable, fence, border, any sort of construction

Dumping some sort of product onto the root area like petroleum products, soap, salt, etc

Change of stormwater flow over the area which may be placing too much water in the area

Leaking irrigation system

Too frequent irrigation

Compacted soil staying too wet

Fig trees are passed along to others by propagating from stem cuttings.

Cut a 6 to 10 inch fig tree stem off the tip of a fig tree stem. Remove all but one leaf. Cut that one leaf in half. Either stick the fig tree stem in the ground where you want the tree to grow or in a flower pot filled with potting soil. Keep the soil moist. Roots grow from the node where you removed the leaves. Once rooted, the stem will start growing.