That's a great question. I think DFAIT struggles with those exact issues almost every day, the issues of how long the term should be and how to ensure that the relationships are passed from one to the other.
One of the ways, for example, is more and more.... It's quite obvious that Canada-based staff are much more expensive than locally engaged staff, so can you hire a cadre of very well qualified local staff who become a bit of a store of knowledge in the location, knowing that they may not have the same absolute loyalty to Canada but that they're pretty good resources?
My wife actually worked as a locally engaged person for a foreign embassy in Washington when we were there, and she served them very well. It's an example of how, if you find the right individuals, they can be a bit of the continuity.
However, that's the ongoing challenge. At a time when budgets are being cut as well, having Canada-based staff abroad is very expensive. We're talking about a quarter of a million to a half a million dollars a head to have people out there.
You're right that there's something to be said for having maybe one more year added to the stay, but the real challenge is the one you pointed out, which is how to actually share all their contacts and relationships. I would hope that perhaps the locally engaged staff might provide a bit of continuity. I've seen some very good local people operate that way.