At the moment If I am bankrupt, a message appears together with the "start new game" dialog. It is still possible to continue the game after clicking away the "start new game" dialog.
I really appreciate the possibility to ignore bankruptcy, however, I would suggest a slightly different behaviour:
After running out of money for three consecutive months, the game should ask me:
"Do you want to:
(a) Start a new game?
(b) Load a game?
(c) Try for one more month? (after which the same dialog should appear)
(d) Keep on playing freestyle?" (without any more warnings)
Just close the new map dialog and you can continue the game.
And of course try run simutrans with -freeplay command. (more at the wiki: http://en.wiki.simutrans.com/index.php/Start_Simutrans (http://en.wiki.simutrans.com/index.php/Start_Simutrans))
Simutrans cannot really handle these kinds of choice dialogs very well. And closing the new world dialog will keep it silent for one month ... YOu can save and reload with freeplay anyway.