Rituals or offerings to Endrborrin would not repair any structural damage to the shrine, but it would help reassure Endrborrin of intent. Since these typically take place outdoors, they would be difficult to perform as usual.

Himeka can use her plant magic to protect the shrine. However this would be susceptible to the same forces that threaten the shrine and would not hold indefinitely. She would need to continue to reinforce the spell and also make sure that there is still access to the shrine.