I've been blessed that I've got more trains than I ever dreamed of when I was a kid. So if they stopped making new trains tomorrow, I'd get by just fine. Nowadays I only buy stuff with new tooling that has not been made before.
I'm still looking for:
Boston and Maine 10-wheeler
Boston and Maine Pacific #3713
Boston and Maine/Maine Central 44 tonner
Maine Central/Portland Terminal Alco HH-660 switcher
Maine Central E7 and 18" passenger cars
Bangor and Arootook E7 and 18" passenger cars
If MTH or Lionel came out with a Maine Central or Bangor and Aroostook F3, I'd be in for more F units, even though I already have several sets of Fs.