People like the drama of the narrative that we could have gone to the wall. It's even pushed by people who were in and around senior levels of the club at the time. However, in my opinion, there's a large degree of hyperbole
Though the sale of Georgi Kinkladze had significantly alleviated our debt problems in the summer of 1998, we lost GBP 1 million on a turnover of GBP 12 million during the Division Two season. We'd have sold Weaver and/or Wiekens to keep the wolf from the door - probably Gerard, who we could have fetched a couple of million for at the time and replaced with Richard Jobson, who missed all of 1998/9 through injury but who played 40-odd league games the next season in the higher division, ensuring performances wouldn't have suffered unduly.
We'd sold almost 14K season tickets before the play-off final, which was not far off the total for 1998/9, so I'd argue that gates would probably have held up well as long as we had a winning side. And we had a team that, if form from Boxing Day to the end of the season had been averaged over the entire campaign, would have topped 100 points.
Of course, you never know how we'd have fared had we been in the third tier again in 1999/2000. However, I think all logic suggests that we'd have had a great chance of winning automatic promotion in front of gates that stood up well compared with those from the previous campaign. Player sales would have kept us financially solvent, if not in an opulent state, without being unduly detrimental to our ability to compete on the field.
This isn't to deny the vast importance of the result going our way that day. Various circumstances suggest that it's highly unlikely we'd be where we are now had Gillingham closed out a win from their position of 2-0 up as the clock ticked round to 90 minutes.
First, Gary James has stated that we wouldn't have moved to the Commonwealth Games stadium had we stayed down that day. Sport England wouldn't have put in the necessary level of funding for a facility with a tenant in the third tier. That would likely have had implications for takeovers in later years. The new stadium was reportedly a significant factor in the takeovers by both Thaksin and, more importantly, Sheikh Mansour less than a decade later.
Second, we also went into the second tier at a very opportune time in 1999, because the second tier the following season was relatively weak. This allowed us to go straight though. By 2000, teams like Fulham, Bolton and Blackburn (all with major financial backing then) had got their act together and were much improved compared with the previous season when we went up under Royle. I don't think we'd have got promoted ahead of those teams, and with our momentum having slowed, we could easily have become stuck in the second tier for years as happened to teams like Leeds, Forest and Wednesday.
Third, and probably the most important factor of all, is the psychological aspect. All of us who were around in the late 1990s know that City somehow seemed cursed - if there was a way to fuck things up, we would. Winning the play-off in the way we did seemed to cast off that feeling at a stroke. I can't prove it, but I'm convinced the way we got up in 1999 created momentum to allow us to be promoted again in 2000. On the other hand, with a loss against Gillingham, even promotion the next season wouldn't have banished the feeling that City would cock things up when it mattered.
So I very much see the Gillingham game as a 'sliding doors' moment: while it's a matter of conjecture, I think the case is quite compelling that, without our comeback that day, the club's current position would probably be very different. On the other hand, to suggest that it stopped MCFC going to the wall is over the top in my opinion.