I know that I cannot use real car models in a game without permission. However, I am interested in a classic (vintage) cars from era before 1950. Some of the companies no longer exist, or were bought by some other company and this by some other company etc. Some cars had custom-made chasis on top of a "skelet".
How is licensing for those cases? Same as for "today" cars, or is there any exception? Something like books where from certain date there are no longer copyrights.
The licensing issues are almost certainly basically the same; copyright law is older than 1950 and there are issues of trademarks, design patents, and trade dress to potentially account for as well.
Working within them will likely be harder, because tracking down who actually owns the rights to older, seemingly-abandoned car designs will probably be difficult.
If you can find and document (or get an expert to do so, preferably) that some car design and associated IP was transferred into the public domain, you can use it. But you should not assume that just because it is "old" or that the company "no longer exists" that the car is in the public domain. Usually when companies cease to exist, whatever assets (physical and intellectual) they had at the time are transferred or sold to other parties.