If you're considering buying off a VW main dealer the Das Welt warranty is said to cover any timing chain tensioner/ component failure, timing chain failure and any consequential damage from such failure.
You could negotiate the revised tensioner and components to be replaced as part of the buying deal and if done by a VW main dealer, such work, aside to your 12 month Das Welt VW approved used warranty, would be covered (parts and labour) for 2 years from the date of the remedial work being done.
Or alternately, given that you're buying with the knowledge of this being a potential issue, then factor in approx £350 for an independent specialist to do it and perhaps try to use it as a negotiating tool for a reduction in the price of the car, if the seller won't do the work for you before you buy.
My understanding and interpretation is that people seem to have more confidence
...once the work is done and should then not be overly concerned about a future failure.