I've saved my game just as a big dwarven caravan entered the map. It entered quite close to my main gate. However, there's something in the path, a dead goblin pehaps, that is scaring one of the merchants and making the whole caravan go away. There are many alternative paths to the trading depot, if the caravan would just choose another route it could reach it with no problem.
However, I don't have a lot of time to build obstacles in the way, or dig/channel/flat the passage preventing their arrival, etc. I also tried to restrict the traffic, but didn't work (probably because the wagon's path was already set). I tried a few times, will keep trying (with burrows, etc), but I'm afraid I won't be able to create an obstacle in time. Is there any other way to persuade the caravan to change path in a short notice? Without making it give up and go away from the map?
Best Answer
I know this doesn't do too much good after so long, but I want the question to have at least one answer.
As the caravan is not part of your civilization, there are only a few things you can do to alter its pathing. All of them involve changing its environment. There are several environmental factors you can change.
The landscape over which it tries to move. This can be anything from building walls, to digging pits to retracting bridges. If you have two entryways that are closable closing one might affect its path, so long as both allow it to reach your depot. However if these systems are not set up already then it would take some time.
The goal towards which it is moving. That is if you were to relocate your depot then the path it would take to reach said depot could change. This however is risky and would probably take more time than you have stated that you have.
The offending object. If you had the time you could move the offending object. Maybe mark it for dumping and set the Dwarves collect refuse from outside option on (command sequence o-r-o (the last o toggles outdoor refuse collection and leaves you in the menu reached by the o-r keystrokes)). (and make sure you have a dumping zone). This is the fastest available option without having prepared it ahead of time.
Timetravel. Due to the unfinished and somewhat buggy nature of the game, many people turn on autosave with backups. If you are willing to savescum, and backtrack to the beginning of the season and you have backups you could use those to timetravel and fix the problem early.
Unfortunately once units are on the map it is very difficult to herd them where you want them to go unless you have more direct control over them (as is the case with your dwarves), or they will run from your dwarves. Neither of these applies in this case.