Yes he can withdraw his vakalat by endorsing on the vakalat " No objection" and handing over it to his client. and also you will have to send regd., A.D. notice to the clinet regarding the withdrawl of the case, which is also known as retirment from the case.
Yes, advocate can withdraw his vakalatnama at any point of time. But, he should endorse "no objection" on vakalatnama and should send intimation of his retirement before proper time to his client (Regestired Post AD is recommended). And after sending intimation, advocate should declare his retirement to the concerned court.
if the client is not co-operating with the advocate and never turn to advocate's chambers. the advocate should issue notice for retirement to the client it should sent through RPAD and it should has to serve on him after that he can be retire from the matter by filing the memo before the Hon'ble Court