Pot lights? You don’t mean grow lights for marijuana, do you? I would have a whole different answer for that question. If you mean recessed fixtures, then I would definitely have the electrician put a new junction box over the new dining room table location and remove the old junction box. It would be cleaner if he could run electrical directly from the dimmer to the new location instead of using the old junction box as a junction point. Otherwise, you can get stuck with that cover plate left in the ceiling for as long as you live in the house.
Another option is to put a recessed fixture where the original junction box is now located. The electrician could use the recessed fixture as a wire-way (feed point) to connect the new dining room light to the original switch. It would mean, though, that the recessed fixture would come on at the same time as the dining room fixture. You could also consider motorized mirror ball there. It would go great with your pot lights.