Can an employee ask for severence pay instead of returning to work after a leave of absence

Can't give you specific legal advice, but as a general matter . . .

As is often the case with respect to benefits, it depends on the specific terms of the benefit plan. Here, if the severance plan (or policy) allows you to terminate directly from a LOA and collect severance, then, obviously, the answer is yes. If it doesn't, then no. But the point is that in almost all situations, severance is contractual -- it is whatever the employer has promised -- nothing more, nothing less. So you have to know what the specific terms are. And they will vary from company to company, and sometimes from employee group to employee group within the same company.