It's totally personal preference, I think. I would not choose to see a T who stated they'd be leaving soon. Even though I don't necessarily need/want to see someone weekly for long-term therapy (I've seen my T twice in the last 6 months...) I also don't like an artificially-imposed timeline.

We did this in my first course of therapy ("let's plan to stop weekly sessions in 15 weeks unless something comes up.") and I wasn't able to engage at all. I just kept counting down the weeks, getting progressively more anxious that I wouldn't be "ready" by the deadline, and finally shutting down entirely because, well, what was the point in getting into something if I wasn't sure I'd be done with it by X date?

But that's just me.