Elizabeth,
To start you should not use dojo.connect it replaced by dojo on.
As of Dojo 1.7, the preferred way of handling events is to use the new lightweight dojo/on module.
For compatibility reasons, the dojo.connect api’s will remain fully supported through remaining 1.x releases, but will likely be removed in Dojo 2.0. Migration from connect() to on() should be straightforward as the api signature is very similar.
If you create a handle in your widget for the map on click event you can remove the event listener by using mapClickEvt.remove() on widget close and or deactive.
The proper way to do this in code is:
this.own(this.mapClickEvtHandler = this.map.on('click', lang.hitch(this, function(){
})));
onClose: function () {
this.mapClickEvtHandler.remove();
},