Quick Advice
Hi Liz, I guess it depends on a few factors. In the current game are you already a co-GM? If you are not the you won't have the GM functionality of adding new players, creating threads etc.
The next thing I would be interested in is your plans for the game. Does the game work GM-less (as you are doing now)? Does it work with two players or would more players work?
I'd also sound out the other player and ascertain their interest in carrying on elsewhere. And there is also the current GM to consider. Have they just abandoned your game or abandoned rpol altogether?
I also think you need to consider your own enjoyment if you want to be a player still in the game if you GM as well. Depending on the game you may lose the ability to be surprised!
I am sorry if I have given you more questions than answers! To sum up, if the game works between the two of you as-is then it may be better to carry on. Your biggest risk is the original GM turning up and deleting the game / threads, changing the direction you want to go in.
If you want control over the scope of the game then starting again may be best although you lose the history of your current game (unless you already are a co-gm then you can download the history and save somewhere).
I'm not coming from a position of massive experience but I hope this helps Liz.