Parker entered the 2014 season as one of the Chiefs top cornerbacks. When Sean Smith was seemingly demoted this offseason, it was Parker who stepped in and ran with the first team at cornerback. Smith eventually got his job back but then Eric Berry got hurt. So it was Parker who stepped in at safety. After his return from injury, Berry's season was soon over with his Lymphoma diagnosis. Parker again stepped in at safety to man the full-time role.
Parker's versatility was quite the sight this season because I did not expect it at all. I wasn't exactly high on him as a cornerback entering the year, although he did have experience at safety too. After Berry was hurt in Week 2, I wrote that it's not reasonable to expect Parker to perform at the level Berry did, and that losing Berry for any period of time would be "horrible" for the Chiefs. Obviously it wasn't ideal but Parker did a very nice job in his role. That's why he deserves to come back.
We don't know what will happen with Berry this offseason -- Berry is entering a contract year anyway -- so it's important that the Chiefs have some sort of insurance policy, lest they enter free agency with a need at safety.
The thing is, Parker has to come back at the Chiefs price. The Chiefs are paying a lot of money in their front seven (with more to come) so they need their secondary to be cheap, which usually means young. I would entertain the idea of going to the draft to replace Parker but that's a risky move considering the draft comes after free agency.
I really have no idea what kind of cash Parker can command but if the Chiefs can get him at a reasonable rate, they need to do it.