So,

As known, there are many "games" that started as mods, once upon a time.

I'm interested in finding out what all would be required to do this legally.

I'm asking about the business & legal requirements of such a process, not a discussion on how likely that is to happen for my case.

As well as having a discussion about any key "games" that would be good examples to look into.

Doubtless we've all heard of Counter strike, and Dota 2, but lets see wich others come to mind, and maybe look at any common challenges or themes they had to deal with.

Also, if you've been involved in making such a product, I'd be very interested in hearing how you got rid of what I'd call "load baring designs", that needed to be taken out / replaced for the core foundations of the new "game" to become a true stand alone., vs. a total conversion or total overhaul.

The business and legal requirements vary from engine to engine.

If the engine and the game are well documented with open and obvious routes to modding it, and the developers encourage you to adjust and mod their game, chances are they expect it and have plans in place.

My advice would be to get in touch with whoever writes the game you're modding and ask them what you should do.

If you're asking for more general advice, this is the advice i would still give first and foremost.

Yeah, in general, get in touch with the makers of the game/engine that you're modding, and ask them about licensing the engine (and any of their game assets that you're also using).

Counter-strike got bought out by the company that made the original game is was a mod for - same with Team Fortress and Day of Defeat :)

The DOTA situation is a bit weird. HON and LOL were attempts to recreate the original mod as a stand-alone game, and simply kept the gameplay while reinventing the IP.

DOTA 2 is a complete recreation of the mod from scratch, on a new engine, but based on the original IP. This is a grey area, and they're being a bit brazen...

Natural Selection 2 recreated their game from scratch on their own engine, rather than trying to license the engine that their mod was built off.

There's also IP problems within your own team. If a volunteer has made a model for you and then left, never to be heard from again... you don't actually have the rights to sell or even redistribute their work. You need to have contracts with everyone from the get-go, assigning the IP rights to your company, so your company can sell the work. Without that, you're leaving yourself open to lawsuits from former contributors of the mod. To make the transition, you'd need to track down all your contributors, get them to sign a contract, and pay them out.

There's also IP problems within your own team. If a volunteer has made a model for you and then left, never to be heard from again... you don't actually have the rights to sell or even redistribute their work. You need to have contracts with everyone from the get-go, assigning the IP rights to your company, so your company can sell the work. Without that, you're leaving yourself open to lawsuits from former contributors of the mod. To make the transition, you'd need to track down all your contributors, get them to sign a contract, and pay them out.