[MrMatt]

Be careful if you decide to do this. If you help out & don't have a consulting agreement / contract in place + the correct insurance, etc... then you may find yourself on the hook for any problems that can be pinned on the work you do after you leave.

[jdormit]

I would be very surprised if they let you write code for them without a contract in place. IANAL, but I believe that technically code you write in your own time is your IP unless you've signed a contract saying otherwise.

[MrMatt]

Yeah, that'd be expected (release of IP etc) however, if you're doing this out of a sense of duty to your ex-colleagues, and the business / management have shown a lack of respect for you up to this point, then I wouldn't be surprised if you see scapegoating.

My point was more that I've seen lots of problems attributed to the last engineer out of the door in the places I've worked. If liability isn't taken care of (sometimes there is a separate contract for liability & scope of work apart from the attribution of IP), and you're doing work to "do the right thing" then it may well be a case of "no good deed goes unpunished".