Lucky you don't live in Ontario Canada, its "illegal" to cut down any tree.. As a matter of fact you would have some Tree loving Nazi Govt Unionized worker at your door demanding you pay a fine... That's what I like about the DR, less rules and way less Govt Socialized Unions..
Setting fire to the stump can result in the fire spreading through the root system. Ficus I believe have very aggressive root sysystems, so no saying where the fire could spread to.
I think the best way to totally kill this tree which really should be called a noxious plant is to use ROUNDUP ,undiluted on the trunk ,,maybe drill a few holes to put the ROUND UP in and then put some over it as it can also kill birds