Edit: Nevermind, see below
I wanted to see how my network would fare over time so put freeplay on (as I'd already discovered I was liable to go bankrupt) put it on high speed and left it for an hour or so. I also added 2 goods AIs and 1 passenger AI since I wanted to see if they would help me.
I checked it every so often, enough to find the good AIs first used routes that were of no use to me and the passenger AI just competed with me.
Anyway I digress in about 1960 I found I was over 1.6 million in debt which surprised me since although my net worth had been going down slightly (I guess because of depreciation of my assets) my cash position had been either stable or even improving slightly (was -450k and reached about -400k at one stage). I then looked in detail and realised most of my buses had disappeared in a number of lines although others still seemed okay. What happened here? I came across one post which suggested that player vehicles disappear if stuck for a long time (similar to city ones), is this what happened? Unless I'm mistaken there's no vehicle breakdowns/crashes and the fact the vehicles were many years obsolete doesn't matter a great deal in Simutrans standard except that there are likely better ones available. I don't believe vehicles have a kilometre or any other lifespan do they?
Cheers
Er nevermind worked out what was wrong. Somehow my vehicles/convoys got detached from the lines, possibly when I updated the lines. I forgot to look at the vehicle list