Actually, if we want to get technical about all of this, no one OWNS OS3.9 except Amiga.inc, we own the media it is on, and the boxes/documentation, but the OS itself we only licence, the £30 is the fee for that license.
Technically he could legitimately just pull a copy of the OS3.9 iso off the web and use that, as his licence is still valid - one copy for one computer (at any given moment). But without the proof of either the reciept from softhut or having registered, it would be increadibly difficult to prove that you do indeed still have that right, so it may well be in your best interest to simply purchase another copy of the OS just to be on the safe side of things.
