u have to ask your maid 想边日走, then you don't need to buy the open ticket.
remember, you must write it down on a paper( the date she wanted ), and let your maid sign it and make a copy for you and she. in case she change her mind.
As I know, even if you asked her and let her sign the paper. In case she changed her mind and not leave at that specified date, the air-ticket is then invalid, you have to buy her a new one, as in the contract you have to provide her an open-ticket in which she can change the date or refund if she wants.
I, myself, do not buy open-ticket for finished contract helpers before, as each separation is peacefully. But still, there is a risk if she 反口.
for this question, I phoned Immigration Department, the answer is: even buy an 14 days (she can stay in HK max. for 14 days after terminate the contarct) open airline ticket, if the helper break the law, over stay in HK, the employer still need buy another ticket to helper back home.
I asked officer, there is any document can see , he told me that in the contact 7.(a), I asked it is unfair because I has already bought an 14 days open ticket and this is under the legal requirement time. the officer said: yes , it is a little unfair, but .........
so before I bought ticket I asked helper which day she want to leave and there is no change for the ticket, also ask she signs on the paper.
Finally I bought it through the agent!! becoz the ticket is all FULL until mid May!! can you believe this?????
I ended up buying the air ticket thru agent, cost $2550...
I ask her to sign a letter declaring she will collect the ticket in agent place later and she need to black and white about the departure date and destination city..just to be safe that she will change her mind later..