It's the same with every big situation, The only team that can stop Bayern, is Bayern. There could be a period where Bayern spends all their money on some players that turns out to be bad, and then they would be stuck with bad players on long and expensive contracts, they will try to fix that and spend more the year after to get better, and then get bad ones again, and suddenly you look and you are terrible.
This could very well happen, it is not impossible and we could see this happen again, it happens in other leagues all the time. So they need to make sure their transfers are good, and they are not making low return on these, otherwise it would be terrible. We could of course be careful with our betting but I bet they will win most their games this year.
Such cases are often preceded by internal club problems, leading to a coaching change and several players eventually leaving the team. After that, a scenario like the one you mentioned occurs. It is indeed not impossible, but Munich is likely to avoid such mistakes for a team that is very large and dominates the Bundesliga. If it is solely due to poor player purchases, we see similar things happening at other big clubs as well.