Is there any stump left ? if there is drill holes in it, put in some "Root out" cover with plastic bag to stop it being washed out and let it do its work.
put an ad in the local paper for metal detectors WANTED SOMEONE WITH A METAL DETECTOR AS I WAS TOLD THERE WAS TREASURE HIDDEN UNDER THE TREE WHEN IT WAS PLANTED WILL GO 50/50 IF ANYTHING FOUND ( outcome you get your tree stump dug up for nothing but a nice mug of tea and buiscuits will keep them going lol
If it's a stump, you could leave it-it will attract wildlife. But if it's in the way, drill a hole in it and pour in some creasote-it'll then rot and dissapear.