According to ([1]), the nuke warheads were safely transferred to Russia:
"Kazakhstan formerly had 1,410 Soviet strategic nuclear warheads placed on its territory and an undisclosed number of tactical nuclear weapons.
...
Kazakhstan transferred all of its Soviet-era nuclear weapons to the Russian Federation by April 1995."
"Kazakhstan formerly had 1,410 Soviet strategic nuclear warheads placed on its territory and an undisclosed number of tactical nuclear weapons. ... Kazakhstan transferred all of its Soviet-era nuclear weapons to the Russian Federation by April 1995."
1. https://www.nti.org/analysis/articles/kazakhstan-nuclear-dis...