No, you can't control my character regardless of whether or not I eventually become able to participate in this RP or not. That's kind of a big breach of RP etiquette, especially thinking you could do that without even bothering to consult me because I 'left' without me saying anything on the subject. Even if the GM had agreed to it which thankfully she did not, I would've been kind of insulted by the lack of respect that demonstrates towards me and the character I created.
While I'm glad you like my character enough to want to do that, I'm disturbed by the lack of respect it shows. If you wanted to control my character, you should have come to me about it rather than going over my head to the GM because I was 'busy with Advanced' and as multiple people have pointed out The GM has no claim on my character. If I am still unable to participate in this RP then the character I made for it will likely go unused. If anyone were to control him, it would probably be the GM as an NPC at their discretion as I have given them more details regarding the character.