The op amp driving the MOSFET won't need to go to 0V. It only needs to go as low as necessary to turn the MOSFET off and 50uV is fine for that. Yes, the input offset probably looks terrible when you set the op amp up as a voltage follower and ground the input but that isn't a factor here.
Hey Jack,
Hope you don't mind answer few questions regarding this topic :
1. Regarding the op amp for driving mosfet, looking at the mosfet gate capacitance, is it "generally" safe to say that its "better" to use op amp that has an output that capable of driving load with quite big capacitance ? or its not a big deal at all ?
2. In the case driving the mosfet at most of the time within linear region in this specific application, will high slew rate op amp (high speed) helps ?
3. By using choper op-amp as OP planned, will the switching noise inside the op-amp affect the regulation loop ? I mean will it amplify/propagate it at the final current loop on loading the DC supply in form of noise/ripple ?
@Spikee, sorry for hijacking, hope you don't mind. 
BravoV,
I probably don't know any more about these things than you do but here's my opinions regarding your questions.
1) I don't think having an op amp with a low impedance output is that big off a deal in this case with regards to bandwidth. I did some simulations and parametrized the output impedance and it didn't really help with bandwidth. The problem seems to be that you still have to use a sizable resistor on the MOSFET's gate to get stability and a lower output impedance didn't seem to allow this to be made smaller.
2) Yes, if high bandwidth is necessary then the op amp's slew rate and gain bandwidth product are going to be big factors.
3) I don't have any thoughts on this. I've never played with choppers.
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