It is possible for a mediocre DM to learn to become a good or even great DM with time and patience. It is exceedingly rare for an adult to learn to be a better person. So, forget Gary and move on.
Some thoughts about Ted, though:
- Firstly, it makes a big difference
why his games aren't up to scratch. Is it because he just isn't very good at DMing? Is it because he doesn't really want to DM, but feels he should because someone has to? Is it because he just doesn't have the time?
If it's the first cause, then you can work with him to improve the game. If it's the second or third, then he's probably not the guy to run the game long term. In this case, you should either rotate the DMing duties and require everyone to take a turn (to see if there's a 'natural' amongst the group, or at least someone who actually enjoys it), or advertise for a new DM.
- Next up, from the OP it seems like Ted's basically taken over the existing campaign, with the existing world, the existing PCs and the existing storylines.
If this is correct, you should immediately wrap up the campaign and start over. By trying to carry on, all you're doing is weighing Ted down with a whole lot of unfair expectations. He isn't Gary and he's never going to be. Let him start fresh.
- Also, you expressed a preference for "sandbox" games. In my experience, these games are harder to run (and much harder to prepare) than more scripted games. An Adventure Path would be a better choice (where "War of the Burning Sky" is regarded as the best of the existing 4e paths).
But, actually, even that is rather ambitious at this point. I would instead recommend that Ted should start by running an
adventure or two, to get used to running games. Then he should graduate to building/running an interconnected campaign, and not really consider a sandbox until he's comfortable with running campaigns generally.
Start small, learn to walk, and then try to run.
