I made 4 test case batches:
- Dried chickpeas, soaked for 24 hours
- Dried chickpeas, soaked for 24 hours, frozen, then thawed
- Canned chickpeas
- Canned chickpeas, frozen, then thawed
I tested with canned chickpeas even though it's well known that they don't work well for falafel so that I'd be able to provide more points of comparison.
I started with the dried but never frozen chickpeas, and it went great! No surprises there.
Next came the previously frozen chickpeas. The consistency of the batter made with them was, as far as I could tell, practically indistinguishable from that made from the never frozen chickpeas. When I deep-fried them it seemed like they bubbled more, so maybe freezing them resulted in the chickpeas holding onto less water. The batter held together just as well as the batter made from the never frozen chickpeas. After eating some of both types, I think the falafel made from previously frozen chickpeas were a bit drier, but still good.
Finally came the (never frozen) canned chickpeas. The batter had a finer consistency than the other ones. When I put the first ball of batter into the oil, it began bubbling much more than the previous ones, and within about 45 seconds the ball had broken apart, and had seriously dirtied the fry oil. I tried again with another ball, this time a bit smaller, and made very carefully, but the same thing happened. After that I called it off, since the canned chickpea batter clearly wasn't working. I made the (small amount of) remaining batter into patties, and shallow-fried it. It was edible, but it wasn't falafel, and so I can't meaningfully compare it to the falafel - at least it didn't go to waste.
In conclusion, falafel can certainly be made using previously frozen chickpeas. It may be a bit drier than falafel made using never frozen chickpeas, but is still quite good, and it comes with the added convenience of being able to soak the chickpeas in advanced.