Does your Miraak remember anything from his life before his entrapment in Apocrypha? I like to think mine does, but only small flashes and snippets. I can just imagine him and the LDB wandering through the ruins of Saarthal and Miraak seems to walk through the ruined halls and corridors like he knows the place. Or perhaps it's Labyrinthian where these flashes of his past first happen. I'd imagine it'd be bittersweet for him, things have changed so much.
I generally agree - after thousands of years, he likely only remembers general concepts and little snippets that can be triggered back to his awareness. Like, the memories are still mostly there, but his brain isn’t making all the connections anymore after so long, so they’re kind of in storage, so to speak, and a trigger can bring them out again (if only briefly). Mostly I’m projecting here, because that’s how my brain works with the amnesia I have about my childhood due to CPTSD.
I picture him wandering through Dragon Cult ruins with the LDB, feeling simultaneously familiar yet foreign, like there’s a memory scratching at the back of his mind that he just can’t fully recall. They unearth a room that’s been locked for thousands of years, and a whiff of ancient incense gives him the briefest glimpse of himself pacing a grand hall, swinging a censer and reciting some litany, but then it’s gone just as quickly as it came.
Sometimes the LDB asks questions about the Cult, and he can recite bits and pieces of information, but he’s not sure how much is from actual memory and how much is from history books he read to pass the time in Apocrypha. It all leaves him feeling strangely hollow.