If the tyre tread wasn't over the limit, then its not a fail - might not have much life left, but not a MOT fail. "Slight knock" over "big bumps" doesn't sound out of the ordinary to me. My Freelander has had all sorts of knocks and bangs over the years, I give them time and they've all gone away! Its 19 years old, I've had it 7 and I've never replaced a mount, bush, drop link etc. When you start getting "big knocks" over "little bumps" - that might be a time to start worrying
As for the props being removed. Its a toss of a coin as to whether there's any serious issues with the car.
They are removed surprisingly often for reasons that aren't due to a trashed transmission. Often they are removed because the support bearings start grumbling (its cheaper to remove that replace). Sometimes they are removed when diagnosing problems that turn out nothing to do with the 4WD, but are never put back on. Sometimes they are removed because the tyres are mismatched or the VCU is shot - but before any real damage is done. Sometimes people may just remove them because they believe they will get an improvement on MPG - which in actual fact is negligible. All of those types of reasons mean you can make sure you have 4 matched (make & model) of tyre and a good VCU and then reinstate the 4WD without any problems.
However, they are often removed because they've been running with mismatched tyres or an overly stiff VCU and it has trashed the rear diff or, more likely, the front IRD. Does it still have the rear pinion on the IRD? If it hasn't, that answers the question, its knackered. If the rear pinion is still on it, you can change the oil and see what the old oil looks like - if its grey, thats the bearings from your IRD ground to a pulp and suspended in the oil - its knackered. If it comes out looking like oil then it might be alright - or the last person just changed the oil! You'll need to see if there is slack in it, maybe disassemble it and examine, etc to determine if its strong/healthy enough to reinstate the 4WD.
As he didn't tell you about it, I'd say he's hiding a problem!