Are demiliches just husks with no memories?

I did some minor snooping about liches and one idea popped into my brain for a enemy idea "what if an old friend of the party (npc) turned into a lich for a noble reason and when he started to feel his humanity slip he stopped looking for souls to turn dormant and fade away without causing trouble"

Now of course if a lich stops feasting they turn into a demilich and thats what this encounter is for. So do demiliches retain memories like the lich or do they just become floaty skelebones?

Tl;dr when liches turn into demiliches (the weaker kind) do they remember anything?