If not THE question regarding independent watches.
We have to consider several factors.
First of all, if it's simple or complicated watch.
The simplicity for example, due to its architecture is a very simple watch and a very robust one.
I think that even in 50 years, we wil able to find someone who will be able to service the watch or even better to "make" a spare part.
But with very complicated calibers, things are not the same.
Several examples come to my mind :
the "needles" system of Urwerk
the hour system of Hautlence
the specific caliber of the HM1
and so on...
Second factor : the strategy of the brand.
I discussed with Dominique Busser from Urwerk about this topic.
He told me that Urwerk produces a lot of spare parts to prepare the future and that they are focussed in creating a company with a continued existence.
I must confess if I'm confidend with Urwerk, that's not the case with some other brands. We have to consider that I met several watches which were not able to run 2 weeks without a trouble...
Fr.Xavier