Each Browser instance is running in a separate native process where the web page is rendered. Sometimes this process can exit unexpectedly because of the crash in plugin. To receive notifications about unexpected render process termination you can use RenderListener. When you receive notification about render process termination you can display a "sad" icon like Google Chrome does, for example, to inform the user that this particular Browser component has crashed.

browser.addRenderListener(new RenderAdapter() {
    @Override
    public void onRenderCreated(RenderEvent event) {
        System.out.println("Render process is created.");
    }

    @Override
    public void onRenderGone(RenderEvent event) {
        System.out.println("Render process is gone:");
        TerminationStatus terminationStatus =
                event.getTerminationStatus();
        System.out.println("Termination Status: " + terminationStatus);
    }
});

If you refresh or load the same or another URL, the render process and Browser instance will be restored. Example: 

browser.addRenderListener(new RenderAdapter() {
    @Override
    public void onRenderGone(RenderEvent event) {
        Browser browser = event.getBrowser();
        // Restore Browser instance by loading the same URL
        browser.loadURL(browser.getURL());
    }
});