My crown fell off and there is little remaining tooth. What are my options for treatment?

I had a root canal done six years ago. Months later an abcess developed and the dentist drilled through the crown to administer treatment, then put in a filling. Recently the crown fell off. The dentist feels that there's not enough remaining tooth structure to recement the crown (though the crown still fits and it doesn't seem that there's been ongoing decay). His main concern is the filling, which goes through the crown and into the remaining tooth structure. What are my treatment options?