Well I wanted to speak about multiplayer, I have some suggestions and ideas... but as I was bit afraid to speak about once I'm not a programmer....

I didn't read entire topic you have linked, but I suppose that a player (Player 0) can open a game and other players can join into (Player 1, 2, 3...and so on). Player 0 is the administrator of game (a.k.a. sever), he is only who can perform some commands that control the course of the game, while others players can perform commands that are necessary for gameplay, just it, nothing more.
If a player went to bankruptcy, Player 0 will inform everyone else that Player X's company went to bankruptcy, and is for sale. Player 0 will use a command that unlocks the failed company (otherwise, anyone could trade their companies any time) to put it for sale. Then, other players would select what they want to. If something remains, Player 0 can liquidate (erase) from map.
But there are some considerations to be taken:
1) For example, if I select just a stop to buy, how would the remaining network run without that stop?
2) How I, who would buy a part of failed company, would evaluate whether I'm buying is interesting?
3) How I, idem, would consult schedules and stats, once I'm wanting to know how the failed company (or the part of) was working until then?
4) Well, I'll expend some money to buy parts or entire failed company. Where will the money go? Player 0? Player who broke their company? (the last one would be interesting).
What'll happen with the player who went to bankruptcy?
Player 0 could either "open" a new company (from scratch) or give back the remaining structure to the player.
For a while, that's all. I'll leave more later.
EDIT: jamespetts, the link is broken.