Came back from 10 day vacation and found my 2008 lr3 hse almost resting on tires. Turned truck on and suspension popped up immediately to normal height. Is this sign to replace pump and /or airbags?

 

It is a sign of a leak. Could be a strut, but could just as easily be a valve block.

 

Is that usually reason to replace entire system or spot treat? I have 195750 very satisfying miles and still going. This is my main rig to tow 17' fishing boat around and want to keep her on the road as long as possible.

 

definitely spot treat
lots of info on this, but it usually boils down to the compressor dryer desiccant becoming powder and fouling the o-rings in the blocks, making them let air back thru

best initial fix that won't break the bank:
step 1, spray soapy water on all fittings to ensure no leaks (bubbles)
step 2, change desiccant and blow out lines
step 3, do the little compressor rebuild kit, I replaced my dryer cap with metal version (my gem had a crack between fittings)
step 4, a month later - open and clean front (and rear) valve blocks - replace o-rings if needed

this refresh could be all you need
search this topic to find more specific info