It's probably possible to develop a mod to save newsletter templates, but I'm personally not all that interested in investing my time in attempting to develop such a mod because I never send out newsletters, sending out bulk or mass emails just has too much potential risk these days of getting you blacklisted by many of the popular email hosts, which means they will bounce any future emails coming from your site until you jump through a bunch of hoops to try and get yourself removed from the blacklists.
You might be ok sending newsletters that are sent to under a 1000 at a time, but once you start getting into sending thousands at a time is were the real potential problems can occur, not just by the email providers that they are being sent to, but your site host might not be too happy with you either, especially if you start getting a lot of bounce backed emails hitting your server, this sets off a red flag with your host.
Most businesses these days use email services for sending bulk or mass newsletters, these services have build a reputation and rapport with all the major email hosts that allows them to send mass newsletters on your behalf so you don't get blacklisted for spamming.
