And even if they didn't, how are the aliens going to decode the data (let alone work out what the data means, without some sufficiently surviving hardware). From scratch.
Even if
not from scratch, see the problems that
The Domesday Project got into within a mere decade or two (and well within the lifetime those that created/experienced it, and their memories)... Compared with the ability to more or less read a (suitably preserved) book/ledger/manuscript/whatever from the
original Domesday project, around a millennium previously (and more extreme examples with ancient clay/engraved writings, though sometimes requiring a Rosetta Stone for assistance...).
If we can come up with a better basic encoding system then
should optical discs decay[1][2], we probably need to arrange for massive... oooh... circles of stone? Lay them out in such a way that even after a lot of weathering the core data can be extracted with enough care and attention to the archaeological detail that should still be available. Let's just hope that nobody mistakes them for astronomical devices or something, eh?
(Plan B: Black monoliths. Let's bury one on the moon and send another up to orbit a different planet. Nothing more needs be said, so could be left featureless, at least on the surface.
)
[1] To be fair, isn't that just CD/DVD-R and -RW that decays? Would a pressed optical media last longer, physical damage allowing? A metal foil surface encased within transparent plastic, basically. As long as the plastic
survives, even if it goes opaque to the usual laser frequencies (and perhaps even warps) someone who knew what they were looking for should be able to use some form of microwave scanning to analyse the embedded data. Might even be able to have a good go at reconstructing a
smashed disc, if not in too many bits (and not too many small fragments lost to the process of analysis) to allow 'static' scanning and then reconstructing back into 'virtual' disc form in order to play it within a player that only exists in software.
[2] They've also recently(-ish) announced a WORM disc writing method which goes back to creating pits, rather than 'temporary' optical alterations in the surface... I heard it was rated to 1,000 years. Above problems with "remembering how to access/interpret it" allowing, of course...