Only succes i have had saving beetle infested trees was with malathion. I get up in the tree with a gallon jug of malathion and pour it between the fronds and truck every frond and it gets into the hole the beetles make. If it dies be prepared to kill the beetles by hand when it comes down.
Instead of cutting and leaving a stump you can spend about an hour or so and dig all around and under the root ball and the weight of the tree will pull out the root ball then you cut it up and fill the hole but no stump left.