It's no different to any other luxury car with air suspension. Complete collapse is not likely to happen just like that, they'll be warnings first in most cases. On the other hand, it may never happen. The other problem is that it's not the kind of system where most garages would have the knowledge to do a quick check. Forget about problems that may never happen, I've had two LS400's but I can honestly say the 430 is by far the best. Having said that, my Lexus days are near an end and being replaced by a Volvo V70....I'd better not say any more or I'll get my post instantly removed again, especially if I mention the "S+++++g" word!
Complete collapse without warning can happen.