Persistent Connections with MONGOOSE - a good idea?

I've made an application enviroment using mongoose and some other stuff which is useful in a nodejs environment. There I have a constructor defined which setup the persistene for each component. Then I thougt (and already wrote some working stuff) is it a good idea to hold the connection persistent to prevent reconnections a lot of times. This is working well (at the moment) but there are two things where I cant find an answear for...

1) Ho can I Handle errors like connection lost (e.g. DB-server goes down)

db.on('error', function(error) {
    console.log('MONGO: ERROR');
    // evt is not fired when DB server goes down
});

db.once('disconnect', function callback() {
console.log('MONGO: DISCONNECTED');
    // evt is also not fired when DB server goes down
});

2) Is it a good idea at all to work with a persistent connection which is done on application start and not on any user request?

All my components extend from my Persistence Layer which establish the connection and initiate the modelName, schemaDefinition etc.

Persistence = function(modelName, schemaDefinition, config) {

this.config = config;

if ( typeof (modelName) === 'string' && schemaDefinition instanceof Object) {
    this.mongoose = require('mongoose');

    if (this.mongoose.connection.readyState == this.config.settings.DATABASE.disconnected) {
        var con = this.mongoose.connect('mongodb://' + this.config.settings.DATABASE.host + '/' + this.config.settings.DATABASE.collection);
    }

        this.modelName = modelName;
    this.schemaDefinition = schemaDefinition;

    var db = this.mongoose.connection;

    db.on('error', function(error) {
    console.log('MONGO: FERROR');
    });

    db.once('open', function callback() {
        console.log('MONGO: CONNECTED');
    });

    db.once('disconnect', function callback() {
    console.log('MONGO: CONNECTION lost');
    });
      }
 };