Once you demote that Domain Controller, it will become a Member Server.
NOTE: Here I assume that you have other(s) Domain Controllers available for that Domain. If that Server is the only/last DC for that domain, you’ll *need* to promote another server to DC and transfer to it all 5 FSMO roles BEFORE demoting it.
And yes, user profiles will still be available after that.
Please post back if you need further help.