Your HSA 100% belongs to you -- there is no recoverying it because it belongs to you already -- they can't take it back -- it is nonforfeitable. (Unless there was some type of admin mistake where you were given too much)

They owe you nothing for pay on unpaid leave....FMLA gives no paid leave, so I dont' see where that would be negotiable.

You can always try to negotiate anything, but they can pull the severance package offer and leave you with nothing but a possible claim. And honestly I don't see retaliation if they have a company policy that you have been trained on regarding giving information out to someone that you KNEW wasn't the authorized user, an employee, etc.

When you are in a pickle, I always tell employees to keep themselves and their work squeaky clean.... because you handed the employer a legitimate reason to terminate you....even if you think it was retaliation, all they need is ONE reason why it is not and they have that. (And what happened to the other employee doesn't really matter especially if they followed all company policies to give out the account password -- they can claim unwittingly doing so , whereas yours seems deliberate). Plus you gave out information that now can be used against them by this user/mother.