Very useful circuit, whoose idea is to make equal Vds voltages of two pmos, which results in ideal current matching. Amplifier is just used to set DC voltage gate voltage of current current mirror gate. So I see this circuit like ideally matched current mirror.
If you want to calculate resistance you can to put at node X Itest current generator and find Vx (R=Vx/Ix). If A is high, negative feedback makes that Vtest=V+=V-. As a result of matching, both pmos will have same current, and output resistances, and through RoB will also flow current Ix, which makes V-=-RoB*Ix.
Then Rout=-RoB.
In the case of finite amplifier gain, I have used symbolic circuit solver Syrup for Maple.
Rout=-ro*(ro+RoB+A*gm*ro*RoB)/(gm*ro^2*A-ro-RoB)