I'm thinking of a realistic scenario for Donner Pass, taking into account the length of the route:
You start with the SP City of San Francisco in Sparks in 1949 with streamlined cars pulled by two Alco PAs.
You get
stranded in snow in 1952 for five days and are rescued by snow blowers.
Reaching Truckee in 1955, your old PAs are replaced with brand-new EMD E9s. A few elderly passengers have died and are taken off the train. Passenger numbers kept steady by new births.
Cisco, CA, 1971. Amtrak has taken over. Your engines are repainted.
Emigrant Gap, 1973. Your ancient E9s are replaced with EMD SDP40Fs.
September 1976. A splits occurs in the community when Cars 11, 12 and 13 elect separatist mayors. Cars 11 and 12 are left in Dutch flat. The Vistadome colony in Car 13 has elected to stay but has fewer and fewer communication with the outside train.
You reach Colfax in April 1982. You have to be helped out of the cab and up into your new EMD F40PH. Violence erupts as long-time residents resist eviction from the streamlined cars into new Amfleet cars. Emissaries failed to contact Car 13, so it is just reattached at the end of the train.
May 1990. A new generation in Car 13 has taken over, explorers have found and opened the door to Car 10. Early contacts were tense, but border crossings are now frequent and your ambassador is well received. There are talks of reunification.
Newcastle, CA, June 1993. Your retirement ceremony ends in a proud moment as you watch your son take command of the brand new GE P40DC Genesis. From now on, you will assist him from the conductor's seat. You still retain your title of President but it is mostly honorary now. Migration to Superliner cars went smoothly this time, as you made sure school teachers properly prepared children, who then helped their parents and grandparents with the move. Clever.
You finally reach Roseville on October 13, 2005 but neither you nor your passengers remember why.