Regretfully their day will come again, the forces of darkness will see to that. I doubt however they will ever dominate in the way the did in the days of the other "purplenose". Whilst the premier league flourishes and rich men use it as a playground others will have the means to at least compete with them not just here but across Europe.
If football goes as I suspect and we end up in a global club set up at some point in the future there will be many who can compete with them from places such as China Russia and of course the USA to name a few. I think they have had their finest hour though sadly a Sunderland type plummet into obscurity is a dream to far I think.
In the meantime we can enjoy the fact that they are so far behind us that even the "mind the gap" joke doent cover it really, as the Grand Canyon is closer to the truth.