Are you asking whether you should call Navigate() and then exit or wait
until documentComplete has fired and then exit?

I've written a web crawler in C# that calls Navigate and then goes into
a loop (yielding via Application.DoEvents) waiting until
DocumentComplete is fired.  At that stage you can call your call back
delegate.

Here's the sample code:
using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;

using mshtml;

namespace WebBrowserNavigator
{
/// <summary>
/// Summary description for Form1.
/// </summary>
public class NavigatorForm : System.Windows.Forms.Form
{
private AxSHDocVw.AxWebBrowser axWebBrowser;
private System.ComponentModel.Container components = null;
private System.Windows.Forms.Label lblStatus;
private bool documentComplete;

public NavigatorForm()
{
InitializeComponent();
}

public string NavigateTo(string url)
{
SetStatus("NagigateTo " + url);
string html = null;

documentComplete = false;
Goto(url);

const int MAX_WAIT = 50000;
int counter = 0;
while (! documentComplete)
{
counter++;
SetStatus("Waiting " + counter);
Application.DoEvents();

if (counter > MAX_WAIT)
{
break;
}
}

SetStatus("Checking title");
IHTMLDocument2 htmlDocument = (IHTMLDocument2)axWebBrowser.Document;
if (htmlDocument.title != "Cannot find server" && htmlDocument.title !=
"No page to display")
{
html = htmlDocument.body.innerHTML;
}

Application.DoEvents();

return html;
}

private void SetStatus(string message)
{
lblStatus.Text = message;
Application.DoEvents();
}

private void Goto(string url)
{
object o = null;
axWebBrowser.Navigate(url, ref o, ref o, ref o, ref o);
SetStatus("Goto " + url);
}
/// <summary>
/// Clean up any resources being used.
/// </summary>
protected override void Dispose( bool disposing )
{
if( disposing )
{
if (components != null)
{
components.Dispose();
}
}
base.Dispose( disposing );
}

#region Windows Form Designer generated code
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
System.Resources.ResourceManager resources = new
System.Resources.ResourceManager(typeof(NavigatorForm));
this.axWebBrowser = new AxSHDocVw.AxWebBrowser();
this.lblStatus = new System.Windows.Forms.Label();
((System.ComponentModel.ISupportInitialize)(this.axWebBrowser)).BeginInit();

this.SuspendLayout();
//
// axWebBrowser
//
this.axWebBrowser.Enabled = true;
this.axWebBrowser.Location = new System.Drawing.Point(4, 4);
this.axWebBrowser.OcxState =
((System.Windows.Forms.AxHost.State)(resources.GetObject("axWebBrowser.OcxState")));

this.axWebBrowser.Size = new System.Drawing.Size(424, 264);
this.axWebBrowser.TabIndex = 0;
this.axWebBrowser.DocumentComplete += new
AxSHDocVw.DWebBrowserEvents2_DocumentCompleteEventHandler(this.axWebBrowser_DocumentComplete);

//
// lblStatus
//
this.lblStatus.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
this.lblStatus.Dock = System.Windows.Forms.DockStyle.Bottom;
this.lblStatus.Location = new System.Drawing.Point(4, 37);
this.lblStatus.Name = "lblStatus";
this.lblStatus.Size = new System.Drawing.Size(248, 16);
this.lblStatus.TabIndex = 1;
this.lblStatus.Text = "Ready";
//
// NavigatorForm
//
this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
this.ClientSize = new System.Drawing.Size(256, 57);
this.Controls.Add(this.lblStatus);
this.Controls.Add(this.axWebBrowser);
this.DockPadding.All = 4;
this.Icon = ((System.Drawing.Icon)(resources.GetObject("$this.Icon")));

this.Name = "NavigatorForm";
((System.ComponentModel.ISupportInitialize)(this.axWebBrowser)).EndInit();

this.ResumeLayout(false);

}
#endregion

private void axWebBrowser_DocumentComplete(object sender,
AxSHDocVw.DWebBrowserEvents2_DocumentCompleteEvent e)
{
SetStatus("Document complete");
documentComplete = true;
}
}
}