DC gain from Nyquist Plot
If it is a type 1 system, it follows that the steady-state error is \$0\$, from which it follows that the DC gain will be \$1\$.

As an example consider \$\frac{3}{s (s+1) (s+2)}\$, whose Nyquist plot is similar to the one you have. The closed-loop system is \$\frac{3}{s (s+1) (s+2)+3}\$. In the limit as \$s\$ approaches 0, it will be \$1\$.

More generally, consider a type 1 system \$\frac{k \ n(s)}{s \ d(s)}\$. The closed loop system is \$\frac{k \ n(s)}{s \ d(s)+k \ n(s)}\$. In the limit as \$s\$ approaches 0, it will simplify to \$\frac{k \ n(s)}{k \ n(s)}\$, which is \$1\$.

The system is type 1, because as \$\omega\$ decreases towards 0 the plot has goes to infinity almost along the imaginary axis. This is characteristic of a type 1 system.