Assuming "ficus pumila" is the creeping fig that clings to walls like ivy, I can report s similar effect with a creeping fig that has taken over our old post and rail side fence in Brisbane. It too is exhibiting die back in largish patches. It is decades old and is quite heavy in parts but the surviving parts have thrown their usual long shoots (up to 60cms) which I will prune back soon. I will need to inspect the fence to see if the "dead" patches are connected to the living - don"t want to cut them off from the roots. I have other ficus growths that are surviving in light shade, but dense shade does see the leaves drop, with the branches seeming to seek out better light. Maybe water is an issue - it was dry here for a while. But I wouldn"t want to water ficus that is growing near the base of a wall - it is after all a fig tree albeit in a creeeping form and fig roots might well be a threat to foundations.