ManageRetries.cs

private async void btnExpireToken_Click(object sender, RoutedEventArgs e)
{
    _token.AccessToken = "GARBAGE";

    var response = await RetryMethod<dynamic>(GetAccounts, 3, 0, RefreshToken);
}

private async Task RefreshToken()
{
    var auth = new AuthenticationClient();
    await auth.TokenRefreshAsync(ConsumerKey, _token.RefreshToken);

    _token.AccessToken = auth.AccessToken;
}

private async Task<dynamic> GetAccounts()
{
    var client = new ForceClient(_token.InstanceUrl, _token.AccessToken, "v29.0");
    var accounts = await client.QueryAsync<dynamic>("SELECT id, name, description FROM Account");

    return accounts;
}

RetryMethod.cs

public async Task<T> RetryMethod<T>(Func<Task<T>> method, int numRetries, int retryTimeout, Func<Task> onInvalidTokenAction)
{
    var refreshToken = false;

    T retval = default(T);
    do
    {
        if (refreshToken)
        {
            await onInvalidTokenAction();
            refreshToken = false;
        }
        try
        {
            retval = await method();
            return retval;
        }
        catch (ForceException ex)
        {
            if (ex.Message == "Session expired or invalid")
            {
                refreshToken = true;
            }
        }
    } while (numRetries-- > 0);
    return retval;
}