Your chance of being rejected is very low. For a large employer like HSBC, they are very used to dealing with IMMD and vice versa--in your case it would be about as close to a formality as it gets.
After all you have considerable work experience AND a postgraduate degree. Better than me (degree but no work experience in my case), and I got a visa!
If you're worried, just ask your HR department about the proportion of successful visa applications for cases like yours. They will tell you. Of course it will come with boilerplate that IMMD has the discretion to do what it wants but once you assure them you're not looking for a legal guarantee they should be very forthcoming about your chances and their past experience with the process.
As for resigning--did you sign the contract with HSBC yet? If you've agreed your start date with HSBC then yes, you should give notice to your current employer.
If you're on sufficiently good terms with your supervisor, just talk to him/her about the situation. For instance my supervisor has been known to accept back-dated resignation letters. If it's not TOO back-dated, he can just say he got behind on his paperwork and HR will never know.