In Michigan, my parents had to rout out the line about once a year, and it was pretty easy to do themselves. One inexpensive tool from Home Depot and you're back in business. Being that I am not sure how the whole thing works, your yad might not have as easy of a fix.

Honestly, $1500 might be the additional cost to cut the tree down, have the stump removed and re-landscape the area to get rid of the sink hole. You can try to fill the pit yourself, but you may have to make a couple of goes over the next couple of years.