I repotted my little succlent (?) a couple weeks ago, and the roots were an awful color of brown. However I wanted to remain optimistic because it's been with me for about 4 years and told myself maybe they're just brown.
So now here I am a couple weeks later and the other 2 cacti are having growth while this little guy remains the same. The thing is it hasn't changed colors over the years, so it's hard for me to tell.

Be patient. Unless the base was soft and gooey, even if for some reason the roots weren't good this plant should put a whole new set of roots. Go really easy on watering while you wait and let it get near dry all the way through. When there is new growth and some of the old growth begins turning green again, you'll know it's likely growing new roots. Sometimes it takes a long time for the process of growing new roots to take place. Nothing in the photo indicates to me that the plant is dead, so even those brown roots may have been good ones.

Won't it be better to cut the top part off and plant it separately?