Hi, 

The cobwebs are unrelated to the tree dying and just spiderwebs. Spiders are just taking advantage for the leaf structures and leaf debris can get caught in them. 

The dead and dying branches are common on Japanese Maples when they are under stressful condition. We can see that it is near the driveway or sidewalk. This means it has root competition and heat stress in the summer. Did you supplement irrigation last year with our drought conditions? Is it buried too deeply in mulch? Japanese maples are susceptible to Botryosphaeria cankers which is a blight that can occur from drought stress and uneven watering. Trees and live with Botryosphaeria as long as they are maintained and not stressed further. 

You can prune out the dead and dying branches as needed and supplement watering in times of drought. 

Emily

you're welcome!

You can review our Botryosphaeria page for more information. 

No fungicide will be useful in preventing the infection; instead, focus on what made the plant vulnerable in the first place and prevent that, which is often drought stress. 

Emily

Thank you for the clarification.

you're welcome