If people are allowed to have one insta-50, make it a time-limited thing. For the first month or two only, and then gone. Or make it a cash-shop option (but keep it cheap, like $10?) so you don't have first-time players doing it and getting overwhelmed.
You have to remember, there's a lot of people who have never played the game before that would be picking it up if it came back. Pushing them instantly to the level cap is going to cause a lot of those people to drop the game rather quickly because there's not a lot to do in the endgame that matters to a player that's skipped the entire buildup through other zones. City of Heroes is a game that's not really about endgame. It's about leveling new characters. There's an endgame to further improve your favorites, but most people had dozens of heroes and villains. You don't want new players to get the idea that this is a WoW-style endgame-focused game because it's pretty lacking in endgame content if you compare it to other MMOs on the market. Keep them focused on leveling new heroes.
What might work better is offering people the ability to skip to lv20 or lv30 on every hero instead of lv50 on one hero. I'd still time-limit it though.
The rest depends on the business model. People won't want to pay again for something they bought, even though it may have been from another company than owns the game if it relaunches. Players don't care- it's a simple fact. They bought it, they want it. So I'd recommend that any powersets, archetypes, and costume pieces from the cash shop just all be granted to all players. As new costume sets or pieces are made(assuming new content is produced), those can be sold to players later on. There's already some that were finished or very close to finished that never made it off of the test server, so those could be sold to players right away with a relaunch and I don't think anyone would complain. Though, again, that depends on the business model.
The cash shop should focus on just offering monetized boosts initially. 200% XP, 200% Inf, etc. Those are things people can buy over and over, so they're important to have to keep the game healthy. CoH had a generous leveling curve so it won't feel like any sort of pay-to-win to have those around.
People will be willing to pay for things, but they won't be willing to pay for stuff they already bought. That's the key thing. Make all previously-available content available for free, charge for future powersets, archetypes, costumes, etc. That's the best way to approach it, and it gives new players a LOT more toys to use than they had in the original's F2P model.