From everything I’ve seen and experienced, Ryanair treats each leg separately, even if it’s under the same booking reference.
They’re not like some legacy airlines that auto cancel the return if you no show the first flight. With Ryanair, if you miss the outbound, you’re just marked as a no show for that segment. The return should still be valid.
That said, I’d still check in for the return as normal when the window opens, just to be safe.
I’ve done similar before and had no issue flying the return, but curious if anyone’s had a different experience recently.