Retailer will not extend its four-year sponsorship deal after England's next winter tour of India.
The 31-year-old batsman is confident the team can repeat their success of 2010.
The 25-year-old bowler is the surprise inclusion of the squad for March tournament in India.
Root blasted a career-best one-day score of 125, but it was not enough as the Proteas win by seven wickets.
Trevor Bayliss' side lead five-match series 2-0 after winning with 3.4 overs to spare at St George's Park.
England hit 399-9 to take the lead in the five-match series.
The 25-year-old batsman is hoping to be picked up by a team in this year's player auction.
The 32-year-old is troubled by a shoulder problem, but the injury is not thought to be career-threatening.
England lose seven wickets for just 49 runs in a little over an hour as Proteas wrap up quick consolation win.
Tourists close day four of the final Test at Supersport Park on 52-3, needing 330 to secure an unlikely win.
England's chances of remaining unbeaten on their tour now look slim.
Captain Cook and Joe Root put on an unbeaten 60-run partnership to deflate the hosts.
Cook hit 115 before England took four wickets at the Centurion.
The world number one Test bowler is recalled after Plunkett withdraws with a thigh strain.
33-year-old Highveld Lions batsman Stephen Cook looks set to make his debut alongside Dean Elgar in Centurion.
The 29-year-old star has climbed to the top of the rankings after a stunning display against South Africa.
The 26-year-old developed the problem during the third Test match in Johannesburg.
England's coach has hailed the performance of the 29-year-old seamer in Johannesburg.
Root reaches ninth Test century to help put England within 75 runs of South Africa's 313.
The seam pair take two wickets each as the tourists make inroads into South African batting line-up.
The 35-year-old batsman has revealed he is relishing life as a freelance T20 cricketer.
Fast bowler has also been named in the reduced 14-man party set to contest the ODI series in February.