Maybe. Probably not people. And not without some incredibly fine control and gobs of computing power. The hard limit is atmospheric conditions on Earth.
According to the Rayleigh criterion, the resolution of a circular collector is a function of wavelength, diameter and distance.
resolution = 1.22 x wavelength x distance / diameter
To detect individual humans from above, let's say we want 50 cm resolution. Alpha Centauri is 4.3 light years away. The Earth's atmosphere is pretty transparent to visible light. How big does the mirror have to be?
diameter = 1.22 x wavelength x distance / resolution
diameter = 1.22 x ~500nm x 4.3 light years / 50 cm
Your telescope has to be 4 light minutes in diameter or half the diameter of the orbit of the Earth. Oh dear. That's ok, all is not lost!
Fortunately you don't have to make bigger and bigger mirrors to get the job done. Others have mentioned multiple array telescope concepts. It can get weirder.
SciShow recently did a piece on space telescope concepts to drastically improve resolution without having to build bigger and bigger mirrors. One is a giant umbrella which would take advantage of the diffraction of light waves around the edge of an object to focus the light.
The other is to carefully position glitter ... sorry... "smart dust" to form a giant mirror in space out of what are essentially tiny reflective pixels. The light pressure from lasers would be used to carefully nudge the particles into position and keep them there.
Then you have the problem of focusing a planet going around the Sun at 30 km/s in a elliptical orbit. That means you don't just track it in a straight line, you have to track the curve of the orbit as well. Once you do that, you have to track a person on the surface rotating at 450m/s, again curved. The math isn't that hard, and since you're so far away you have to turn your telescope very little, but the minute and constantly changing motion of your telescope required is extremely difficult to resolve down to a few meters.
This is why we don't point the Hubble at the Earth. DSCOVR, the recently launched telescope we do intend to point at the Earth, will sit at the Sun-Earth L1 point 1.5 million km away and is only intended to do atmospheric readings.
Fortunately for our 4 light minute wide space telescope, this is all predictable! Each piece can focus their local element individually without having to communicate with the rest of the telescope. No internal FTL communication required.
Atmospheric conditions are your ultimate limiting factor, the problem of atmospheric haze. Even on the clearest day, the atmosphere reflects and diffuses light making your image fuzzy no matter what you do. This is part of the reason we put telescopes in space. But it is mostly transparent to certain wavelengths. Visible light is one. Microwaves are much better, but humans and aircraft carriers don't emit microwaves. Also the longer your wavelength (microwaves are pretty long) the lower your resolution.
Scientists have been studying the problem of how to get good resolution through an atmosphere for a long time and have come up with some very, very clever ways to overcome the problem. The whole is covered under adaptive optics. But that's for looking out from inside the atmosphere. We want to look in.
Fortunately we don't have to run the numbers, we have had spy satellites which can do this since the 60s and 70s. They're good enough to see aircraft carriers and people through the atmosphere, a sufficiently large array at Alpha Centauri probably is, too. But I don't have the numbers.
The other place to look for information is in speculation about viewing exoplanets.
You will be seeing 4.3 years into the past. You might think "great, then I can see whatever caused the Earth to stop communicating years ago", no. Information can only travel at the speed of light, so your information that there is a problem on the Earth would also be 4.3 years old. Even if at the moment you realized there's a problem on Earth you swung your super telescope to look, you'd still have missed the event. Best you can do is see the aftermath.
What you can definitely do is gather data to theorize about what happened. For example, if you see a lot of atmospheric dust that could indicate meteor strike or nuclear war. Spectral analysis could tell you if there's a sudden increase in any elements in the atmosphere. Changes in albedo could tell you similar things. Color shifts could tell you if there was a massive plant die off (or if it goes the other way, Triffid attack). This is how we make guesses about exoplanets right now, just from a few smudged pixels.
With all that time and effort to get what will probably be a hazy image of what happened 4 years ago (plus time to make and focus the telescope), it might be best to just pack up the family car and take a road trip. Of course by then it will have been at least 8 years. But at least you can pick up souvenirs.