Former enterprise software sales person here (now in operations, having to deal with the kind of crap I used to give the ops group :D).
I agree that any salesperson worth their salt would keep a list of the contacts they have cultivated professional relationships with.
However, if (as it seems from the tone of the OP) this is a list of contacts that the company provided to the sales rep, well, this is a bit trickier. If they went to OneSource, or Hoovers, and bought a list for a specific territory, then handed it over to the rep and said “go sell stuff”, how long until the rep truly “owns” the contact? A month? A year? Three years?
Maybe Nanoda can elaborate on the situation. Is this a company-purchased list (or even a list of existing customers)? Is the rep an inside or outside rep? Fielding inbound calls primarily, or cold-calling, or somewhere in between? What kind of product do they sell, and what “touch-level” is required to sell it (executive level/middle management/operations)? What level of effort is required by your employer to let them keep this list? Is it simply a rolodex? A CRM report? A database with confidential data that requires scrubbing?
As for differentiators (commission/salary, fired/quit) - if they are purely salaried, with no significant variable pay attached to their sales, I wouldn’t call them a sales rep. I would call them a customer service rep. If your paycheck is the same whether you sell stuff or not, you don’t own a business relationship, you’re just serving as the face (or voice) of your employer, and have no right to any customer list.
If they were fired with cause, I would send them packing with nothing more than what they came in the door with - it’s bad business to reward bad employees. If they quit, or were laid off without cause, I might let them have something, depending on the level of effort required by your employer. Unless they went to a competitor - then, I’d probably turn them down as tactfully and politely as possible.
At the end of the day, it boils down to the consequences of granting or denying the request. Are you in a small job market where word gets around of bad employers? Or are you in a super-competitive space, and need any business edge you can get?