I didn't research it fully, but the chem pack is build into the reservoir tank starting on models around 2004. It is the same coolant I use on older car with 2 years change recommendations. In California I always give coolants 5 years.
So as far as I know you can not buy Mercedes chem pack separately and the owners of the cars with it will have to change the tank with the pack every 15 years. That is not coming in next 7 years, so we don't know what might come on the market before.
Than on my motorhome I use lifetime coolant from FleetPride. That stuff doesn't require any chem pack, but is used on diesels with build in filters with SCA balancers.

 

you have to watch with the filters that have DCA in them. change the filter too often and the DCA level gets too high. that is when things get all snotty and plugged up. otherwise it does work well.

 

Well I had to replace mine on an 2006. F350 6.0 just 2 months ago and now my new one just cracked . lucky I made it home. Just drove to vegas and back. I do haul things with my 40ft gooseneck. So the age doesnt really matter. Glad it has a lifetime warranty on it.