Is Task.ContinueWith() guaranteed to run?

Suppose I have some async task that can sometimes run fast and sometimes slow,

public Random seed = new Random();
private async Task<string> _Work()
{
    int time = seed.Next(0, 5000);
    string result = string.Format("Worked for {0} milliseconds", time);
    await Task.Delay(time);
    return result;
}

public void SomeMethod()
{
    _Work(); // starts immediately? Am I right?

    // since _Work() will be executed immediately before ContinueWith() is executed,
    // will there be a chance that callback will not be called if _Work completes very quickly,
    // like before ContinueWith() can be scheduled?
    _Work().ContinueWith(callback)
}

Is the callback in Task.ContinueWith() guaranteed to run in the above scenario?