Will I have problems getting a discontinued auto brand or model repaired or getting parts once it is out of production?

 

What car do you have?

 

I've never had problems maintaining 20-30 year old vehicles, and some of my cars teh manufacturer had been bought out 20 years previously.
Volume of vehicles still on the road is your best guide to parts availabiltiy, often an older model will share significant amounts of parts with other vehicles by the same manufacturer and even share parts with other manufacturers.
If there is a market for spares, someone will produce them.

Regards, Andrew.