Firstly, your "in an instant" is faster than light and that means it is principally impossible.

Secondly, I doubt such powerful telescopes are possible even theoretically. Some hypothetical beings might be looking an our galaxy from that distance but how many PHOTONS from Earth reach them? I suppose not enough to even suspect Earth is an object.

If you were 70 million light years from earth at this moment you'll see dinosaurs (if you can find an instrument that can see in that detail from that far).

But even if you were able to travel 70 million light years away at the speed of light you'll actually see earth how it was strait after you left at light speed.

Of course you know you can't travel at light speed. so you will never be able to see the past. Theoretically if you can travel from one point in space to another faster then the speed of light (maybe throw a worm hole) you can see a past earth.

I hope I answered your question.