If they sing off key consistently, meaning they just can't sing, then they don't deserve their success. If they are just off-key occasionally, that's fine.
They're more than welcome to stay (I still voted that they shouldn't be in the industry), though they'll be nothing more than a reminder of why I appreciate my fave so much.
If you don't possess any talents that make up for that flaw, I think you should find a new profession. Leonard Cohen isn't a great singer, but his songwriting makes up for that.